Alfred Piggott 2012.05.31 Compressed Air Vehicle Report Comparison Diesel Electric Gasoline Thermal

MEEM 4200 - Research Project

Air-Powered Vehicle
Homework Group 1

Team Members
Seth Brezee
Stephen Buckley
Alfred Piggott
Andrew Schorfhaar

Compressed Air Energy Conversion Compared with Battery Electric, Gasoline and Diesel

1.0 Abstract......................................................................................................................................................... 3
2.0 Introduction ................................................................................................................................................. 3
3.0 Conversion Technology Level Analysis................................................................................................... 5
3.1 Serial Efficiency - Fossil Fuel to Engine Output ...................................................................................... 5
3.1.1 Compressed Air Serial Efficiency ........................................................................................................ 5
3.1.2 Battery Electric Serial Efficiency.......................................................................................................... 8
3.1.3 Gasoline Serial Efficiency ................................................................................................................... 11
3.1.4 Diesel Serial Efficiency ........................................................................................................................ 11
3.1.5 Summary of Serial Efficiency ............................................................................................................. 15
3.2 Carbon Footprint ......................................................................................................................................... 16
3.2.1 Compressed Air Conversion Carbon Footprint.............................................................................. 16
3.2.2 Battery Electric Conversion Carbon Foot print .............................................................................. 16
3.2.3 Gasoline Conversion Carbon Foot print.......................................................................................... 17
3.2.4 Diesel Conversion Carbon Footprint................................................................................................ 17
3.2.5 Summary of Carbon Footprint........................................................................................................... 17
3.3 Conversion Technology Cost..................................................................................................................... 18
3.3.1 Compressed Air Motor Conversion Technology Cost................................................................... 18
3.3.2 Battery Electric Motor Conversion Technology Cost.................................................................... 18
3.3.3 Gasoline Engine Conversion Technology Cost .............................................................................. 20
3.3.4 Diesel Engine Conversion Technology Cost................................................................................... 20
3.3.5 Summary Conversion Technology Cost ........................................................................................... 21
3.4 Energy Density ............................................................................................................................................. 21
3.4.1 Compressed Air Energy Density ....................................................................................................... 21
3.4.2 Battery Energy Density........................................................................................................................ 22
3.4.3 Gasoline Air Energy Density.............................................................................................................. 23
3.4.4 Diesel Air Energy Density .................................................................................................................. 23
3.4.5 Summary of Energy Density............................................................................................................... 23
4.0 Vehicle Level Analysis...................................................................................................................................... 24
4.1 Vehicle Cost .................................................................................................................................................. 24
4.1.1 Compressed Air Vehicle Cost ............................................................................................................ 24
4.1.2 Battery Electric Vehicle Cost.............................................................................................................. 24
4.1.3 Gasoline Vehicle Cost ......................................................................................................................... 24
4.1.4 Diesel Vehicle Cost .............................................................................................................................. 24
4.1.5 Summary of Vehicle Cost ................................................................................................................... 25
4.2 Vehicle Range ............................................................................................................................................... 25
4.2.1 Compressed Air Vehicle Range.......................................................................................................... 25
4.2.2 Battery Electric Vehicle Range........................................................................................................... 26
4.2.3 Gasoline Vehicle Range....................................................................................................................... 26
4.2.4 Diesel Vehicle Range ........................................................................................................................... 26
4.2.5 Summary Vehicle Range...................................................................................................................... 27
4.3 Advantages and Disadvantages .................................................................................................................. 27
4.3.1 Compressed Air Vehicle Advantages and Disadvantages.............................................................. 27
4.3.2 Battery Electric Vehicle Cost Advantages and Disadvantages...................................................... 28
4.3.3 Gasoline Vehicle Cost Advantages and Disadvantages.................................................................. 29
4.3.4 Diesel Vehicle Cost Advantages and Disadvantages ...................................................................... 29
5.0 Conclusion ......................................................................................................................................................... 30
Bibliography ............................................................................................................................................................. 31

Homework Group 1 12/10/2010 Page 2 of 34


1.0 ABSTRACT

In our world today we rely on petroleum probably more than any other resource available for
energy, especially for means of transportation. However, this form of energy conversion is
contributing to the production of greenhouse gasses in the atmosphere and the raw supply is
gradually depleting. Since the invention of the automobile, engineers have been searching for the
ultimate alternative energy source for vehicles that is both safe and less polluting. Today engineers
are focused on battery or hybrid-electric powered vehicles as the green energy option and are rapidly
developing products. However, there are few maverick companies that are also investigating the use
of compressed air as a green energy source.

This research paper will be focused on this new method, vehicle propulsion using on-board
compressed air energy storage. The use of compressed air as a means of clean reusable energy
source in consumer passenger vehicles will be analyzed from a thermodynamics point-of-view. In
addition to an in-depth review of the compressed air energy source, current competing technologies
will also be included. This includes a fossil fuel-to-motor output analysis of battery electric, gasoline,
and diesel powered systems. The comparison will included the cost/kW output for engine or motor,
energy conversion serial efficiency, CO2 emissions/kW-hr and the amount of energy that can be
stored on a specific volume basis. The analysis can then be used to gauge the true “green energy”
propulsion leader at the present time.

2.0 INTRODUCTION

This paper will objectively compare compressed air energy conversion with gasoline and diesel
power conversion as well as battery to electric power conversation. The paper will focus on several
key characteristics of these systems: the cost/kW output, energy conversion serial efficiency, CO2
emissions/kW-hr output and the amount of energy that can be stored on a specific volume basis.
The efficiency and emissions calculations will take into account the power plant and electric grid
delivery if that delivery method is utilized in the process (i.e. using an electrically driven compressor
to charge the compressed air tank). The analysis begins with the fossil fuel at the power plant or the
gasoline refueling station.

Although the primary objective of this paper is to compare the “conversion techniques”, vehicle
level attributes such as the cost, range, advantages, and disadvantages of vehicles with the above
mentioned power conversion technologies will be addressed. Finally, the paper will discuss
limitations with current mass produced air powered vehicles.

Recently in the media there has appeared information regarding a mass produced vehicle powered
only by compressed air (21). While there is media excitement regarding the development, there
appears to be an absence of an objective study comparing the compressed air powered vehicle
propulsion process with other propulsion techniques. The compressed air vehicle proposed would
use energy stored in a compressed air tank and a piston/cylinder arrangement to convert energy into
work, propelling a vehicle. The estimated power scale for a compressed air vehicle would be similar
to production vehicles, which are in the kW range.



CURRENT STATE OF THE ART OR UNDERSTANDING

To understand this technology one must possess basic knowledge of how compressed air is used to
propel a given motor or vehicle. The basic layout of a simple working motor running off of
compressed gas has been patented (34)(35)(36) but a true production application of the system has
not yet emerged and is therefore difficult to collect engineering specifications. Reviewing the
patents, the idea is relatively simple to understand. An air compressor is used to compress gas into a
stored form in a pressure tank. This pressurized air is then used (expanded) in a controlled fashion
to drive the piston of a modified reciprocating engine. There are also other designs that use a rotary
style displacement engine (37). Current designs are a bit more involved than this basic idea but
using the expansion of air to produce work is the core principle of process. In the absence of
production vehicle engineering specifications, the paper will estimate the isothermal expansion
efficiency of the engine based on available pneumatic motor specifications.

Though the basic design is said to be emission free, current working models use fuels to run
onboard compressors and heat the air entering the motor piston, when running at higher velocities
above 35 mph, for extra power (9). Although compressed air vehicles are themselves emissions free,
if they use power generated by an emissions producing plant, the vehicles just displace their
emissions to the power plant. Compressing air on a commercial level would require a tremendous
amount of energy which would likely be produced by fossil fuel power plants, which make up a
majority of US energy production. However, utilizing renewable or emission free power generation
such as nuclear, wind, solar, or hydroelectric to compress the air would likely reduce greenhouse gas
emissions. The same could be said for battery-electric vehicle contributions to greenhouse gas
emissions.

Limitations of current pressure tank mechanical strength have restricted prototype performance.
The longest published test run of a vehicle solely using compressed air was roughly 7 km (8). Motor
Development Industrial (10) has stated that their current model has the capacity to run for up to 135
km at up to 68 mph. While other companies have made claims that they intend to produce models
in the future that can run for up to 1000 miles at up to 98 mph. Though these claims have yet to be
backed by sufficient testing results it does suggest a world filled with cheap and almost emission free
transportation (but is it safe?). Compressed air can be seen as a risky technology because like a
balloon, weakness in the container can lead to catastrophic failure. The current idea to avoid this is
to create carbon fiber matrix pressure canisters that crack instead of shatter or explode to mitigate
some of the risk.

As stated previously the leading company in the air compressor industry is MDI. Their current
working models are called the AirPod and CityCat. Working production vehicles have been
delivered to Schiphol, the international airport in Amsterdam, The Netherlands, for evaluation (40)
MDI also plans to begin production for the US marketplace as early as this year (11) though the lack
of a given refuel infrastructure could prove a difficult sell. As stated previously, current testing
shows only a maximum running distance of up to 140 km, which isn’t a published figure at that (11).
This coupled by the fact that the vehicle needs up to 3 hours to refill without specialized equipment
could impede product sales (11).

Of course gasoline, diesel, and battery electric vehicles are not “perfect” either, each with their own
strengths and weaknesses. This paper will now analyze the efficiency of each system and draw
conclusions.


3.0 CONVERSION TECHNOLOGY LEVEL ANALYSIS

This paper will use a Fossil Fuel-to-Engine Output analysis. Fossil Fuel refers to the fuel supplied
to the power plant, or gallon of fuel pumped at the refilling station. Engine output refers to the
energy available at the shaft of the electric motor or internal combustion engine crankshaft. The
analysis does not include the mechanical losses beyond the output shaft such as the transmission or
final drive to eliminate vehicle-based variables that may skew objective analysis. This paper intends
to primarily focus on the specific technology “conversion” efficiency. In each section it may be
necessary to state the specific technology chosen and the engineering specification for that
component. Where applicable, reasonable engineering assumptions will be made and stated in the
efficiency calculations below.

3.1 SERIAL EFFICIENCY - FOSSIL FUEL TO ENGINE OUTPUT

3.1.1 COMPRESSED AIR SERIAL EFFICIENCY

Serial efficiency was calculated back to the power plant per the diagram below.

Power plant Electric Grid Electric High Pressure Air Compressor Pneumatic Motor

For this study it was assumed that most owners would use electric power to charge the compressed
air tank at home or purchase compressed air from a charging station that uses electricity to compress
the air. Diesel powered air compressors are available but they presumably would not be the norm
due to noise, local exhaust emissions and higher maintenance required over electric units.

The type of fuel and age of power plants varies from region to region in the United States so the
efficiency will vary depending on the region where the compressed air vehicle is being refueled or
“charged”. For this study, average U.S. power plant efficiency was used given the likelihood that
compressed air vehicles would be sold in more than one region. The average power plant efficiency
in the U.S. is 0.35 (1).

The U.S. electric grid has an efficiency of 0.935 (2) and is a measure of what power plants produce
versus what was purchased by consumers as read at their electric meters. The electrical system of a
typical business or residence is assumed to be 100% efficient since no conversion or step up / down
processes are utilized.

Compressed air vehicles require highly pressurized air storage tanks to raise the energy density of
compressed air. The pressure is around 4500 psi or about 310 bar. To charge these tanks, a high
pressure compressor must be utilized. With published compressor specifications (3) the efficiency of
the compressor was calculated to be 0.48 per the below calculation.

Air compression is a polytropic process. If an isentropic (adiabatic) process is one bound for a
compression process the opposite bound is an isothermal process (14) See figure 1 below. From
kinetic theory we know the energy of an ideal gas increases when it is compressed as kinetic energy
is added to the molecules by the compression apparatus for example a moving piston. If the process
is Isentropic (adiabatic), the kinetic energy of the molecules is imparted to the walls of the container



and back to the gas. When compression stops, the gas temperature will remain elevated. During an
isothermal process the kinetic energy imparted on the walls of the container is dissipated to the
environment surrounding the container.

P

P2

1<

n
n= k
<n
<
<k
n=

I
Ise
I
Is

1
1
o
ot

n
ntro
h
he
rm

icp
p
al
P1

V

Figure 1: PV Diagram – Source (14)

For an air compressor the process most resembles an isothermal process. Of all three processes,
note that the area under the curve is the highest for the isothermal process, so more work is done
reach the same pressure as the other processes.

Air Power Output
ηcompressor =
Electric Power Input

p 
Wisothermal = p1V1 ln 2 
p 
 1

For an Isothermal process, p1V1 = p2V2

 p 
So, V 1 =  2 V 2
 p 
 1 

By substitution, this gives

p  p 
Wisothermal = p1  2
p V 2 ln 2
 p 

 1   1 

Dividing the isothermal work by time give the isothermal power
p  p 
p1  2 V 2 ln 2 
p  p 
 1  1
Powerisothermal =
Time



p1 = 1 bar , or atmospheric pressure
P2 = 344.7 bar , the maximum pressure output of the compressor
V2 = 1m3 , the internal volume of the tank
Time = 31.1 hrs, filling time from zero to 344 bar

 344.7 bar  3  344.7 bar 
1 bar 
 1 bar 1m ln 1 bar 
  
Powerisothermal =     = 1.78kw
31.1 hrs

Air Power Output 1.78kw
ηcompressor = = = 0.48
Electric Power Input 3.73kw

To utilize the energy stored in the compressed air tank, a pneumatic motor is required. For this
study, published specifications of a 30 hp pneumatic motor (4) were used to calculate motor
efficiency. 30 hp is in the range (15-50 hp) (12) (13) of what published MDI compressed air
passenger vehicles use. MDI also claims its pneumatic motor applications range from 4 -75 hp. (6)

To calculate efficiency of the pneumatic motor (4), the ratio of rated power input of compressed air
versus rated power output at the shaft was used. The efficiency of the pneumatic motor was found
to be 0.31 per the below calculation.

Shaft Power Output
η Pneumatic Motor =
Compressed Air Power Input

p 
Wisothermal = p1V1 ln 1 
p 
 2

Dividing the isothermal work by time give the isothermal power

p 
p1V1 ln 1 
p 
Compressed Air Powerisothermal =  2
Time

p1 = 6.2 bar , the rated inlet pressure
P2 = 1bar , or atmospheric pressure
V1 = 3.88 m3
Time = 60 sec



(6.2bar )(3.88m3 )ln 6.2bar 
 
Compressed Air Powerisothermal =  1bar  = 73.1 kw
60 sec

Shaft Power Output 22.3 kw
η Pneumatic Motor = = = 0.31
Compressed Air Power Input 73.1 kw

It should be noted that the efficiency at max power may not be the peak efficiency of the motor and
any usage of a motor in the vehicle may use the vehicle transmission to keep the motor at or near
maximum efficiency.

In summary, the efficiencies were found and calculated for each step in the energy conversion
process per the below diagram and the final serial efficiency was calculated per the below
multiplication

Power plant (0.35) Electric Grid (0.935) Electric High Pressure Air Compressor (0.48)
Pneumatic Motor (0.31)

η serial = (0.35)(0.935)(0.48)(0.31) = 0.0487

3.1.2 BATTERY ELECTRIC SERIAL EFFICIENCY

A pure battery electric powered vehicle (BEV) was used for comparison. For a pure BEV, the
following energy conversion takes place:
On-board vehicle components

AC/DC Battery Battery
Power Electric Charging Converter Charging Storage
plant Grid Station Efficiency Efficiency Efficiency

Electric 3 Phase Motor Battery
Power applied Gearbox/Axle
Motor Inverter Discharge
at tires Efficiency
Efficiency Efficiency Efficiency

On-board vehicle components

Figure 2 – BEV energy conversion process

For this efficiency study we will calculate the serial efficiency of the BEV system to the output of the
electric motor. This is the point in the BEV conversion process where the conversion to
mechanical power takes place. Additional process steps are shown in Figure 2 above to illustrate the
full vehicle process, but the analysis will stop once mechanical power is made.



So, to compute the Fossil Fuel to Motor Output efficiency, the following steps will be included:

Power plant Transmission Grid Charging Station AC/DC Converter (on-board) Battery
Charging Efficiency Battery Energy Storage Efficiency Battery Discharge Efficiency Three-
phase Motor Inverter Efficiency Electric Motor Efficiency

Many different methods and business cases are being developed to charge BEV’s, but we will
assume for this study that a BEV customer will choose to charge the vehicle at home overnight.
Other assumptions will be made in the efficiency analysis in regards to individual component
selections. Component selections will be based on currently available technology, possibly already
offered to the consumer.

Component selections used for BEV analysis:

1. Home Vehicle Charging Station: 220 Volt AC inductively coupled
2. Battery Pack: 24 kW-hr Lithium Ion (Manganese Cathode construction)
3. Electric Motor: 3 phase Inductive, 80 kW peak power

For the power plant energy production and transmission line loss, the same values researched for
the compressed air vehicle analysis in section 3.1.1 will be used. The BEV customer, just like the
compressed air customer above, will charge their vehicle at home using a residential supply of
electricity. The following serial efficiency numbers were found in section 3.1.1: Power plant
efficiency = 0.35, transmission line/electric grid efficiency = 0.935.

All BEV’s require recharging from some electrical power source. While there are many different
voltage levels and power ratings available, the most typical high powered source available to the
residential customer will be 208-240 volt AC rated for 30 amps. The standard 110V-15 amp circuit
may also be used, but automotive manufacturers recommend the 208-240 volt circuit and will even
make installation arrangements for the end customer (39). Finally, besides the voltage/current
specification, there is also the issue of how to connect the vehicle to the grid. There are two primary
methods of connecting the vehicle. The first is to use a “conductive” receptacle or charging harness,
the second is to use an “inductive” adapter. The conductive system simply plugs the vehicle into a
special wiring harness and power is applied directly, like a household extension cord. The second
method, the inductive, uses a non-contact method to the transfer the power utilizing two close
proximity inductive coils. While the conductive system is more efficient, the inductive type does not
have exposed wires, contacts, or open connections. Therefore, the inductive type charger will be
chosen for this analysis because it offers all-weather (outdoor) charging capability and will be
perceived by the customer as a safer charging alternative with reduced shock hazard. Currently
published values for the conversion efficiency of inductive charging receptacles is 0.86 (22).

Once the electrical grid is coupled to the vehicle via the inductive charger, the AC/DC converter
must transform the AC current to a DC voltage that will charge the batteries. The AC/DC
converter will also regulate the current and monitor the voltage and temperature levels on the
battery pack and regulate the charge rate. This device is a critical link to the longevity of the battery
pack. Typical efficiency levels for the AC/DC converter are greater than 80 percent, with switch-
mode converters rated at 90 percent (28).



Many types of battery chemistries and constructions are available for BEV use. The most recent
BEV applications are all utilizing Lithium Ion chemistry. Lithium Ion chemistry is a very efficient
method to store electrical energy. Currently published data on charging/discharge efficiency is on
the order of 0.99 percent (23). Although astonishing, this claim is validated by an independent
second reference that experimentally determined that the overall charge/discharge efficiency of a
Lithium Ion battery to be 0.984 (24). The high efficiency of this battery type also has a second
benefit, very low heat rejection during the charging and discharging of the battery.

Lithium Ion batteries are also efficient at storing their electrical charge. Published results for
Lithium Ion battery charge retention is nearly 100 percent, losing only 2-3 percent per month (42).
A typical customer charging their car daily will see no self-discharge. Lithium batteries are memory
free, 100 percent of their charge is available for discharge. However, Lithium Ion battery
performance is affected by ambient temperature. Elevated temperatures increase the self-discharge
rate and may permanently damage the battery, and temperatures below freezing affect the cell
voltage and battery capacity (42). Finally, Lithium Ion batteries do age with respect to the number
of charge/discharge cycles, but this affects only the energy capacity (25).

The charge stored in the battery must be converted to a 3-phase AC current to drive the electric
motor used for propulsion. The electric motor used for this analysis is capable of 80 kW peak
power. Typical gasoline engines are greater than 100 kW peak, but electric motors can provide full
power at zero speed (broader torque band). In contrast, the pneumatic motor used for the air
powered vehicle analysis is on the order of 20 kW, which may be perceived by the customer as
underpowered. The device used to convert the DC battery voltage to the AC waveform needed for
the motor is called an Inverter or Motor Controller. Inverters used to produce this AC waveform
are roughly 96 percent efficient (0.96). Although references could not be found for portable motor-
inverters used in automobiles, equipment used for 100kW commercial applications support the 96
percent claim (26).

The electric motor chosen for analysis is a 3 phase AC induction motor, roughly 80 kW. Electric
motors are roughly 400% to 600% more efficient than internal combustion engines (28). AC
induction motors have efficiency ratings that exceed 90 percent (0.90) in most cases. However,
those efficiency ratings are usually at loads greater than 50 percent. At loads less than 50 percent
motor efficiency rapidly decreases. To be as representative as possible, a motor efficiency was
chosen that was experimentally determined using the Federal UDDS (urban dynamometer driving
schedule) and HWFET (highway fuel economy test) cycles. Although a “vehicle” based test
parameter, it was used to help identify the properly weighted average efficiency. The reported
electric motor efficiency in this test report was 0.804 (24). This is a true measured value, over a fuel
economy test route with a slightly larger induction motor (130 kW).

Now assembling the individual steps necessary to produce the motor mechanical output:

Power plant (0.35) Transmission Grid (0.935) Charging Station (0.86) AC/DC converter
(0.90) Battery Charging Efficiency (0.99) Battery Energy Storage Efficiency (1.0) Battery
Discharge Efficiency (.99) 3 phase Inverter Efficiency (0.96) Electric Motor Efficiency (0.804)



Now performing the calculation we find the serial thermal efficiency to be:

η serial = (0.35)(0.935)(0.86)(0.90)(0.99)(1.0)(0.99)(0.96)(0.804) = 0.1916

It should also be noted that the efficiency of the vehicle to produce power from the battery charge
above is approximately 76 percent. This value is in-line with a US fuel economy website (27)
claiming electric vehicles are 75 percent efficient converting the chemical energy in batteries to
motor power.

3.1.3 GASOLINE SERIAL EFFICIENCY

An Average gasoline engine sedan was chosen for comparison with the compressed air vehicle. The
energy conversion process shown below takes place in this type of system:

Extraction Efficiency Refinement Efficiency Gasoline Gasoline Combustion Engine
Gear Box/Axel Power Applied to Tires

The research objective was set to calculate serial efficiency from fossil fuel to engine output in that
case the only factor in the above flow process that was needed to be taken into account was the
gasoline combustion engine efficiency. This efficiency is a readily known number is in average
around 18%. The diagram below in Figure 3 shows the efficiencies and losses that occur in gasoline
combustion propulsion method. (44)

Figure 3: Efficiency Diagram (45)

As mentioned, the refinement process was not calculated into the serial efficiency. The process
begins with crude oil resulting directly from the ground; through the refinement process of crude oil
products on top of gasoline include petroleum gas, Naphtha, kerosene, diesel, lubrication oil, and
residuals like coke. This process will be more closely examined in the following section.

3.1.4 DIESEL SERIAL EFFICIENCY

The point of comparison in serial efficiency for this paper is to find the efficiency between fossil fuel
to engine output. The fossil fuel in this case being petroleum oil which has to be refined into diesel



before it has a practical application automotive field. As a point of curiosity the efficiency of the
fossil fuel from the well to the motor was calculated. Afterwards these calculations will be modified
to calculate the standard serial efficiency (fossil fuel – motor output) for the purpose of energy
platform comparison. Efficiency mapping for the complete process would go as follows:

Extraction Efficiency -> Transportation Efficiency -> Refinement Efficiency -> Fuel
Transportation Efficiency -> Motor Efficiency -> Vehicle Performance Efficiency

An assumption was made that the extraction, refinement and distribution facility locations were the
same. The vehicle performance efficiency was also excluded because this value depends on vehicle
size and driving conditions, etc.; this was done for the sake of simplicity, these values vary
depending and there isn’t easily available data to create an accurate simulation. And so the following
calculation goes as follows:

Extraction Efficiency -> Refinement Efficiency -> Motor Efficiency

Extracting oil is the result of a pump. An assumption was made that the pump would be run by a
motor-generator unit. And thus the finalized calculation was calculated using the following mapping
method:

Extraction Efficiency (Motor Efficiency -> Generator Efficiency -> Pump Efficiency) ->
Refinement Efficiency -> Motor Efficiency

Oil pumping plants run using large motors, generators and pumps. Larger equipment yield greater
efficiencies than smaller models but for the sake of simple calculations the assumption will be made
that the process will use a standard diesel motor, electric generator and pump. A standard diesel
motor has been known to have rated efficiency values as high as 75% but in practice these models
normally only yield efficiencies between 35 and 40 % (50). This calculation will assume a value of
40 % for diesel motor efficiency.

A typical electric generator has efficiency values between 93 and 97 % (51). This calculation will use
a value of 95%.

Pump efficiency varies greatly and is dependent on the type of pump, wear of the pump, viscosity of
the fluid, amount of fluid being pumped, etc. Below (figure 4) is a graphical representation of the
relation between maximum pump efficiency and pumping output performance; being published by
John M. Campbell and Company.



Figure 4: Pump Efficiency Vs. Pump Capacity
http://www.jmcampbell.com/october-2009.php

It is easy to see that a small pump would yield a very inefficient performance value. Oil companies
rely on efficient processes to ensure substantial profit margins. The assumption of the experiment is
that the small pump used in the process will mimic the high efficiency performance of a standard
pump used in the oil production field. A standard high range value, as can be seen on the graph, is
about 80%.

The problem that arises during calculations is that refinement processes don’t have standard
published efficiency values. Available published data goes only as far as giving an energy balance
ratio; a value that describes the ratio between the energy contained within produced fuel and the
energy used to obtain and refine it. The total potential energy of a barrel of crude oil is 5.8 million
BTU and the energy balance ratio of crude oil is 1/5, being that is takes roughly 580,000 BTU’s to
extract the oil from the ground and roughly the same to process it (53). This is the value need to
process a barrel of crude oil into a plethora of different fuel sources, including diesel. Included
below is a simple graphical model of the refining process.



Figure 5: A Simplified View of the Petroleum Oil Fossil-Fuels Refining Process
http://www.eia.doe.gov/kids/energy.cfm?page=oil_home-basics

Diesel is just one of the many products that can be yielded from petroleum oil. This process is
complicated but it can be noted that the maximum quantity of diesel that can be efficiently created
from a barrel of oil is pretty constant. See figure 6 for a graphical representation of the by-product
quantities created from a standard barrel of crude oil.

Figure 6: Standard By-Products from a Barrel of Crude Oil


http://www.eia.doe.gov/kids/energy.cfm?page=oil_home-basics

A standard barrel of crude oil yields about 10 gallons of diesel. To calculate the energy needed to
refine this quantity of fuel the ratio between the energy input to refine the whole barrel and the
potential energy of the resulting fuel will be compared to the potential energy of the yielded diesel.
Diesel is a heavier carbon chained fuel than a standard fuel like gasoline; this could mean that the
refining process of diesel could be more or less energy demanding. Standard values for diesel fuel
refinement are not available and so calculations will continue on the basis of assumption.

A liter of diesel contains 36.4 MJ (53). A MJ is the equivalent to approximately 948 BTU. And so a
liter of diesel contains about 34507.2 BTU. A gallon is the equivalent of 3.785 liters. And so the 10
gallon yield of diesel from a barrel of crude oil contains about 1.306 million BTUs. The total energy
yield of a barrel of oil is 5.8 million BTU and the energy needed to extract or refine it is 0.58 million
BTU; and so the ration of energy input to potential energy yield is 1/10. And so the energy need to
extract or refine 10 gallons of diesel is about 130,600 BTU.

The minimum energy requirement for diesel refinement is 130,600 BTU plus the energy contained
within the fuel, though the energy output is only the potential energy contained in the fuel. This is to
say that the efficiency of the process is about 81.1% efficient. This goes to say that the overall
efficiency of the process is as follows:

Extraction Efficiency (30.4%) (Motor Efficiency (40%) -> Generator Efficiency (95%) -> Pump
Efficiency (80%)) -> Refinement Efficiency (81.1%) -> Motor Efficiency (40%)

And so the overall efficiency of the process is approximately, 0.9086 %. This value does not include
the fact that the extraction process is an estimate using many assumptions; motor efficiency for the
extraction process is probably greater and pump efficiency is probably worse in reality. Not
including the fact that transportation and secondary refining processes were not included in
calculations.

For the sake of this report the extraction efficiency needs to be excluded as it was not proposed as
an original parameter for the report though it will be important for a more accurate calculation of
the carbon footprint of diesel; which will be discussed in greater detail further along in this report.
The original parameter for serial efficiency is to find the efficiency from the fossil fuel to the motor
output.

The serial efficiency map is as follows:

Refinement Efficiency (81.1%) -> Motor Efficiency (40%)

And so the serial efficiency of diesel fuel from the fossil fuel state to motor output, excluding
extraction and transportation efficiencies, is 32.4%.

3.1.5 SUMMARY OF SERIAL EFFICIENCY

After analyzing the calculations for each technology, it is apparent that compressed air vehicles have
a very low serial efficiency. In fact, Compressed air vehicles have the lowest efficiency of any of the



technologies examined. Diesel engines have the highest efficiency and are unmatched converting
chemical energy into usable power.

As illustrated in the Diesel example, the analysis should have gone back all the way to the well and
accounted for losses in the extraction and refinement of the fuels. A future study should look at the
front end processes to further analyze the energy lost just obtaining the fuel. In hindsight, this will
mostly be important in the estimation of total Carbon footprint.

3.2 CARBON FOOTPRINT

One of the driving forces to develop air powered, or even battery electric powered vehicles, is their
ability, perceived or real, to reduce the production of greenhouse gas emissions. So to contrast the
different propulsion systems even further, this project team decided to calculate the amount of
greenhouse gas emitted by each technology on a per unit of energy basis. The air-powered and
battery electric vehicles derive their energy direct from the electrical grid. The gasoline and diesel
engines derive their energy from fossil fuels. One argument for air powered and battery electric
vehicles is that, as we deploy more renewable energy sources to produce electricity, the greenhouse
gas emissions will decrease. So, to understand where we are today, this team decided to develop real
numbers for each technology. The term “carbon footprint” derived in these calculations relates the
mass, in kilograms of CO2, for each kWh of energy consumed by that technology.

3.2.1 COMPRESSED AIR CONVERSION CARBON FOOTPRINT

lbs kg
In 1999, 1.341 (or 0.608 ) of CO2 were produced on average by power plants in the U.S.
kWh kWh
(7). This takes into account the mix of fossil fuels and renewable sources used for power generation
in the U.S. in 1999.

To evaluate the true carbon emissions, or carbon footprint for the compressed air propulsion
technology, it is necessary to divide through by the derived serial efficiency. This will give us the
cost in CO2 produced per unit of energy utilized.

Carbon Footprint =
hWk 1 rof tnalp rewop ta decudorp OC
2
η
laireS

Using the serial efficiency calculated in section 3.1.1 for the compressed air vehicle, the true carbon
footprint for technology can be found:
 kg 
 0.608 
=
hWk1 rof tnalp rewop ta decudorp OC kWh  kg
Carbon Footprint = 2
= 12.5
η
laireS (0.0487 ) kWh

3.2.2 BATTERY ELECTRIC CONVERSION CARBON FOOT PRINT

Since battery powered vehicles are charged from the grid, the formula is the same:



Carbon Footprint =
hWk 1 rof tnalp rewop ta decudorp OC
2
η
laireS

Using the serial efficiency calculated in section 3.1.2 for the battery powered vehicle, the true carbon
footprint for technology can be found:
 kg 
 0.608 
=
hWk1 rof tnalp rewop ta decudorp OC kWh  kg
Carbon Footprint = 2
= 3.17
η
laireS (0.1916 ) kWh

3.2.3 GASOLINE CONVERSION CARBON FOOT PRINT

Gasoline powered vehicles are one of the major sources of CO2 being let into the atmosphere
resulting of the sheer quantity of them and the many miles they are driven. The Intergovernmental
Panel on Climate Change (IPCC) guidelines was referenced in the calculation of the carbon
footprint (46). The amount of CO2 in one gallon of gas is a readily know number (65), 8.8 kg.
Dividing the one gallon amount by the engine efficiency yields the carbon footprint.

 kg   kg 
 8.8 gallon   8.8 gallon 
Carbon Footprint =   =   kg
= 1.74
 kWh   kWh  kWh
 gallon  ( EFF .)  33.7 gallon  ( 0.15 )
   

3.2.4 DIESEL CONVERSION CARBON FOOTPRINT

The referenced value for the carbon footprint for a liter of diesel is 2.7 kg of carbon emissions (54).
2.7 kg is the equivalent of 5.952 lbm on earth. The energy contained within a liter of diesel is 36.4
MJ (55). The serial efficiency of a diesel motor was found to be around 32.4 % in practice (56). And
so the useful energy in a liter of diesel is 14.56 MJ.

A KW-h is equivalent to 1 KW * 3600 seconds = 3.6 MJ.

And so the carbon footprint of diesel in lbs/ KW-h can be calculated to be, 0.667 kg/kW-h.
But because the serial efficiency is 32.4 %, including extracting efficiencies, the actual carbon
footprint for of diesel to create a kW-h of energy is, 2.06 kg /kW-h.

The carbon footprint can be found to be 1.7 kg/ kW-h.

3.2.5 SUMMARY OF CARBON FOOTPRINT

Examining the results from the carbon footprint analysis for each technology, it was found that
compressed air, and battery electric, vehicles actually produce more CO2 at the power plant than do
gasoline and diesel vehicles at the point of operation. The argument for the compressed air and
battery electric vehicles is that the CO2 is produced at a centralized point, and thus can be treated



more easily. However, they do produce more CO2. As power production facilities move towards
more renewable energy sources, the amount of CO2 will be decreased.

3.3 CONVERSION TECHNOLOGY COST
3.3.1 COMPRESSED AIR MOTOR CONVERSION TECHNOLOGY COST

Cost figures for pneumatic motors used in compressed air vehicles are not readily available. One
would expect the cost of pneumatic motors to be much less than a gasoline engine. This is due the
fact that a pneumatic motor does not need a fuel injection system, ignition system or cooling system.
The basic piston driven design is the same as the internal combustion engine, but due to the reduced
power output of the pneumatic motor, it may be possible to also reduce the weight using thinner
castings or different materials. Finally, since internal cooling passages are not required in the engine
block or cylinder heads, manufacturing a pneumatic motor should be significantly lower in cost.

From various non-automotive pneumatic motor suppliers the price ranges from $239/kw to
$469/kw per Table 1 below.

Cost ($) Output (HP) Output (Kw) $/kw ($/kw) * 0.70 Cost Source
$ 267 1.5 1.1 239 167 (18)
$ 528 2 1.5 354 248 (19)
$ 285 0.75 0.6 510 357 (20)
$ 15,000 30 22.4 671 469 (4)
Table 1 – Pneumatic Motor Cost per Output ($/kw)

The pneumatic motors list above are likely not produced on a mass production scale that
compressed air vehicles could reach, furthermore the pneumatic motor industry in probably not as
cost competitive as the automotive industry. Taking into account automotive economies of scale and
cost reduction pressure, a 30% reduction in cost compared with the pneumatic motors listed in table
1 above would not be unreasonable. Taking into account the 30% cost reduction, the price would
range from $167/kw to $469/kw.

3.3.2 BATTERY ELECTRIC MOTOR CONVERSION TECHNOLOGY COST

In a battery electric vehicle (BEV) there are several specific components that are unique. Simply
stated, an electrically driven powertrain is substituted for the gasoline driven system. Focusing only
on the propulsion system, the BEV must have an on-board charging system for the batteries, the
battery pack itself, the motor controller-inverter electronics, and the electric motor. To support the
system, you must also use a battery containment system, high voltage cables, charge receptacle, and
unique liquid cooling system (for the motor and inverter). Figure 7 shows the necessary
components for electrified propulsion in the 2011 Nissan Leaf.

The following are the unique components selected in section 3.1.2 to support battery electric
propulsion:

1. Home Vehicle Charging Station: 220 Volt AC inductively coupled



2. Battery Pack: 24 kW-hr Lithium Ion (Manganese Cathode construction)
3. Electric Motor: 3 phase Inductive, 80 kW peak power

24 kW-hr Lithium Ion Battery

Motor Controller Induction Motor

Figure 7 – 2011 Nissan Leaf Propulsion Components
(photo source: Nissan www.nissanusa.com)

The cost to install a home charging system for an electric car is expensive. It requires the utility
company to come to your house, upgrade your electrical service, and install the charger unit. While
the price estimates vary for this type of installation, $2000 dollars seems to be a mean amount (29).
That cost is $1200+ for the labor, and $700+ for the charging device. Of course, the cost to install
the charger is dependent upon the customer’s current electrical capacity and service. Figure 8 shows
a typical outdoor inductive paddle type installation.

Figure 8 – Inductive Charging Station
(photo source: GE Wattstation www.ge.com)



The electric vehicle battery pack is the single most expensive component required for an electric
vehicle. Using state-of-the-art Lithium Ion battery technology, which has a very high
charge/discharge efficiency rate, the cost for the batteries alone can cost tens of thousands of dollars.
The challenge today is to find a high efficiency battery that also has a low $/kW-hr cost. That is the
trade-off, kW-hr capacity (range) versus cost. For the battery component chosen for this analysis, a
reasonable cost estimate to use is $500/kW-hr (30). The battery size used in this analysis is a 24 kW-
hr, so the total battery cost is roughly $12,000.00. However, it seems that price is a bit optimistic. A
later report pegs the cost of the Nissan Leaf battery at $750 / kW-hr or $18,000 (33). The Nissan
Leaf Battery is representative of the component chosen for this analysis, a lithium ion 24 kW-hr
battery pack. This price does not include the supporting systems required (battery containment,
cooling, etc…), but it is the majority of the cost. It is also the majority of the cost for the electric
vehicle itself and the major roadblock to high volume mass production of the electric vehicles.

Other costs related to the electrification of the automobile are the charger and motor/inverter
electronics. Electronics typically have a rapid decline in cost once volume production kicks in.
However, both of these devices use expensive insulated gate bi-polar transistor (IGBT) circuits rated
for high voltage and current and are not cheap. An estimate for the charger/motor/inverter
electronics assembly is $2000 in production quantities. A reference could not be found for this cost,
it is a very conservative estimate. The 3 phase induction motor is also rather expensive. A
conservative estimate for the motor is $3000. Although individual references could not be found, a
2009 estimate is available for both the motor controller and the motor at $5000 (31). Since both are
required to run the propulsion system, they will both be used for the cost/kW comparison. For a
system valued at $5000, and a rated power output of 80 kW, that equates to a rough figure of
$62.5/kW for the package.

3.3.3 GASOLINE ENGINE CONVERSION TECHNOLOGY COST

The average gasoline engine costs can vary quite a bit depending on size, performance and quality
but the average stock engine price that receives 30 MPG can be found for around 4 thousand dollars.
On top of that cost there is the cost of the gasoline itself to power the engine, as all know gasoline
prices are a large part of life today. Gas prices are around aver 3 dollars a gallon in the United States
and are fluctuating constantly. This price is cheaper than diesel even though diesel is less expensive
to produce due to demand (46).

An average sedan was chosen to be compared; an example gasoline sedan contains about 190 hp,
with 1 hp equal to 0.745 kW. Therefore, the conversion for the gasoline system with these numbers
is $28.25/kW.

3.3.4 DIESEL ENGINE CONVERSION TECHNOLOGY COST

The average diesel motor costs about $1000 more than the average gasoline equivalent (57). The
average cost of a mid-size gasoline engine that gets 30 mpg is about $4,000 new which would place a
comparable diesel engine at about $5,000 (63).

A standard diesel engine has a maximum power output between 170 (i.e 2010 VW Jetta TDI) and
350 hp (64). A hp is the equivalent of 0.745 kW and thus normal maximum power outputs lie
between 126.8 kW and 261 kW. And from this we can see a conversion technology cost range for a



diesel engine between $ 19.15/ kW to $ 39.42/ kW; though the upper limit is a more accurate
representation of a common diesel engine for a mid-sized vehicle.

3.3.5 SUMMARY CONVERSION TECHNOLOGY COST

Compressed air vehicles will have very high cost when compared on a power output basis.
Although the basic motor cost should be lower than a gasoline or diesel engine, the motor produces
very low power. Battery electric vehicle costs are very high, primarily a result of the battery pack
cost.

3.4 ENERGY DENSITY

3.4.1 COMPRESSED AIR ENERGY DENSITY

The following equation can be used to find the internal energy of a tank of compressed air.

3
U= PV
2
U is the internal energy, P is the pressure of the tank and V is the internal volume of the tank.
For the case of a typical compressed air vehicle, P =310 bar. Since the desired answer is energy
density per unit volume, V = 1 m3 .

3
U= (310 bar )(1m3 ) = 46.5 MJ
2 m3

The energy density in a tank of compressed air can be used along with the isothermal compression
work and the first law of thermodynamics to find the heat transferred to the ambient air during
compression.

∆W − ∆Q = ∆U

Q represents heat transferred from the compressed air during isothermal compression, W is the
work done to compress the air and U is the internal energy of the air.

Rearranging we have,

∆Q = ∆W − ∆U

From the prior calculations we find ∆Q = 178 MJ − 46.5MJ = 131.5MJ

Heat is released during the compression process but heat is also absorbed from the environment by
convection and conduction with the walls of the pneumatic motor during the expansion process.

To improve the efficiency of the expansion process, some compressed air vehicle designs use a heat
exchanger (15) to transfer heat from the environment back to the expanding air while others use a



hybrid design with an external combustion chamber (16) to heat the air in order to add the heat lost
during compression back in during expansion.

3.4.2 BATTERY ENERGY DENSITY

Battery energy density is a readily known parameter. Different types of batteries obviously have
different energy densities. The chart shown in figure 9 provides an energy density reference for
popular battery chemistries. Higher energy densities allow a smaller battery pack to store more
energy and increase vehicle range. For the battery pack design chosen in 3.1.2, Lithium Ion, the
average energy density is 150 W h / kg.

Figure 9 – Energy Densities for Battery Chemistries (source: Nature (32))

Based on the Lithium Ion construction and material, and referencing figure 9 again, Lithium Ion
volumetric energy density is approximately (center of balloon):

300 W hr / liter

300 W hr / liter = 0.3 kW hr / liter
1 liter = .001 m3
0.3 kW hr / liter = 300 kW hr / m3

1 kW hr = 3.6 MegaJoules
300 kW hr / m3 = 1080 MJ / m3
This is the latest production viable state-of-the-art lithium ion batteries and they are still a relatively
poor method of storing energy due to low energy density. Although much better than previous
lead-acid or NiCad technologies, another doubling or tripling of capacity would make electric car
range more viable.

Weight is also important. Although the Lithium Ion energy density is approximately 6 times greater
than previously used Lead-acid batteries, they are still heavy. The 24 kW-hr battery pack in the


Nissan Leaf weighs a hefty 660 pounds (43) with the supporting cables and battery containment
shell. The remainder of the electric car components; the electric motor, motor controller, high
voltage to 12V converter, and cables all approximate the weight of the gasoline engine they replace.
Therefore the Nissan Leaf weighs roughly 600 pounds more than a similar vehicle powered by a
gasoline engine. (43) Overall, the system is heavier, but getting closer to an internal combustion
system weight.

3.4.3 GASOLINE AIR ENERGY DENSITY

The energy density of gasoline is a very readily known number at 132 x 106 Joules/gallon [4]. So this
number could be more easily compared with that of compressed air the units MJ/m3 were chosen to
be used for energy density. Below the unit conversion can be seen:

 Joules   1MJ  1gallon  MJ
Energy Density = 122 x106   6  −3 3 
= 32, 230 3
 gallon   10 J  3.7854 x10 m  m

3.4.4 DIESEL AIR ENERGY DENSITY

The energy density of diesel in relation to mass is comparable to that of gasoline (9). However,
diesel has a higher average specific density (mass per volume) therefore its energy density in energy
per volume (MJ/m3) would naturally be higher.

The referenced value for energy density of diesel with a specific weight of 0.84 g/ml has an energy
density of 36.4 MJ/liter (59).

To convert to MJ/ m3 one must use the following conversion factors:

[ 1 liter ] = [ 1000 ml ]
[ 1 ml ] = [ 1 cm3 ]
[ 1003 cm3 ] = [ 1 m3 ]

And so,

36.4 [MJ/liter] * 1/1000 [ liter/ml ] * 1 [ ml/ cm3 ] * 1003 [ cm3/ m3 ] =

36.4 * 103 MJ/ m3

It should be noted that the density of the diesel product will change the energy density of the
product. That is to say that a denser diesel will yield a higher maximum potential energy value than a
lighter product.

3.4.5 SUMMARY OF ENERGY DENSITY

Compressed air, and electric, vehicles do not even come close to the chemical energy storage
capacity of gasoline or diesel vehicles. This will always be a hurdle for broad acceptance of
compressed air and electric vehicles. The poor volumetric energy density limits the total range these
vehicles can go. One of the issues with the previous generation of electric cars was that customers



experienced “range anxiety”. They were afraid to venture too far from home so they did not run out
of charge and became stranded. Gasoline and Diesel vehicles do not have this issue, plus you can
stop anywhere and refuel.

4.0 VEHICLE LEVEL ANALYSIS
4.1 VEHICLE COST

4.1.1 COMPRESSED AIR VEHICLE COST
Although there are no production vehicles, MDI (Motor Development International) states on their
website (10), a 6 seat, 75hp vehicle will be priced at $17,800.

During a video (11) interview with the Chief Engineer as well as the CEO of MDI (11), The Airpod
model was said to be priced at 3500 Euro ($4600) and another off camera vehicle was said to be
priced at 6700 Euro ($8900)

Other information published by MDI (12) prices the vehicle model OneFlowAIR from 3500 to
5300 Euro ($4600-$7000) depending on whether it is a base or standard model

The ranged of published or announced expected pricing of MDI compressed air vehicles is $4600-
$17,800.

4.1.2 BATTERY ELECTRIC VEHICLE COST

Production electric vehicles are just entering the marketplace. The vehicle most representative of
the Battery Electric components chosen for this analysis is the Nissan Leaf. The Nissan Leaf uses a
24 kW-hr battery pack composed of Lithium Ion cells. The vehicle also uses a 85 kW peak 3 phase
induction motor.

Manufacturer suggested retail cost for the 2011 Nissan Leaf, now just entering the market, is
$32,780.00 (33). It has been reported the vehicle costs more than that to build, but this has not been
verified. It is known the cost of the battery is over half of the vehicle cost as reported above.

4.1.3 GASOLINE VEHICLE COST

As almost everyone is aware a gasoline vehicle can run in price from 12 thousand to over 100
thousand dollars in price. Explained before, research was done on an average sedan in the market
for instance Chevrolet Malibu.

A Malibu has a base price of 22 thousand being around the average for a mid class 4-door sedan.
This vehicle is rated at 23 MPG in town and 34 MPG on the highway with a stock 2.4 liter 4-
cylinder engine with an upgradable option to a 3.7 liter 6-cylinder option [7].

4.1.4 DIESEL VEHICLE COST

Like any type of technology the cost of a diesel vehicle is dependent on the brand, model, size,
potential power output, etc. In general a diesel vehicle is normally priced about $1500 to $2000 more


than a comparable petrol counterpart. As stated previously in this report, this value is due to the
higher cost of the diesel engine. For an average diesel mid-sized vehicle the average base cost will be
around $20,000 but there are diesel vehicles that cost a lot more.

Beyond the cost of the car itself one needs to keep in mind fuel costs. A diesel vehicle gets on
average 20 – 30 % more gas mileage than a petrol equivalent, this is to say that a petrol car that gets
30 mpg can expect to get around 38 mpg with a diesel engine. Today in Ann Arbor price of diesel is
$3.20/gallon which is to say $ 0.084 /mile (60). And then there are maintenance costs to think
about; on average diesel repairs cost about two times the petrol price but diesel motors are known to
outlast most petrol equivalents.

4.1.5 SUMMARY OF VEHICLE COST

Overall, a compressed air vehicle may be very affordable due to the relatively simple architecture.
Battery electric vehicles will remain very high due to battery costs; but they are economical to drive.

4.2 VEHICLE RANGE
4.2.1 COMPRESSED AIR VEHICLE RANGE

Since the energy density of compressed air is so small compared with gasoline and the energy
conversion efficiency of a pneumatic motor is so small, all else being equal, we should expect the
range of a compressed air vehicle to be significantly less than a comparable gasoline powered vehicle.
Information on compressed air vehicle range is difficult to find. The only published test result for a
test in a city traffic condition was 7.22km (8).
Urban Range (miles)

450
408
400
Urban Range (miles)
350

300

250

200
127
150

100
29
50

0
Compressed Air Vehicle Gasoline Vehicle Electric Vehicle

Figure 10 – Drive cycle simulated driving range (source (9))

One study (9), shown in figure 10, simulated the range of a compressed air vehicle, electric vehicle
and gasoline powered vehicle with a drive cycle analysis. The drive cycle UDC (Urban Drive Cycle),
developed by the European Union is comparable to the EPA drive cycle UDDS, but is said to be
less demanding because of lower top speeds and lower acceleration. The vehicle parameters used are
those from published vehicle specifications on vehicle manufactures website. The results of the
driving range simulation are shown in figure 10 above.



4.2.2 BATTERY ELECTRIC VEHICLE RANGE

In terms of range, a battery electric vehicle is dependent on auxiliary loads. Use of the air
conditioning, heater, steering, and any other accessory directly saps battery energy. Many electric
vehicles now include display screens to let the driver know the range every instant as they use their
accessory systems. In fact, the vehicle may also make suggestions how to improve range by turning
off specific loads.

Figure 11 – Nissan Leaf EPA sticker (source: www.nytimes.com)

Again using the Nissan Leaf as an example, the reported range for the vehicle is 73 miles (EPA) on a
full charge (24 kW-hr). In reality, this range will be reduced if the customer uses the heater or
another load, but it representative of a federal EPA cycle range. See figure 11 for the actual EPA
sticker found on the vehicle. The EPA did the math; the Nissan Leaf uses 34 kW-hr per 100 miles.
34 kW-hr is roughly equivalent to 1 gallon of gasoline (1 gallon = 33.7 kW-hr per the EPA), thus the
99 miles per gallon rating of the vehicle.

4.2.3 GASOLINE VEHICLE RANGE

The range of a gasoline vehicle is dependent on the vehicles miles per gallon ratio and the fuel
capacity of the gas tank on board. As stated before this project chose a sedan in today’s market that
on average gets 30 MPG, this type of vehicle usually contains a fuel capacity of around 16 gallons.
The calculation of vehicle range can be seen below:

 miles   gallons  miles
Vehicle Range =  30 16  = 480
 gallon   tank  tank

4.2.4 DIESEL VEHICLE RANGE

An average diesel engine is rated to get between 20 to 30% higher gas mileage than the average gas
vehicle (61). This goes to say that for a standard tank size a diesel vehicle would out performance a
gas-based counterpart in maximum traveling distance.



The gas mileage of a VW Jetta TDI 2010 is rated at 42 mpg highway (62). With the assumption that
the car has a small tank size of around 12 gallons (the tank size of a 2001 Ford Focus) the car would
have a maximum traveling distance of 504 miles.

This value really relies on the size of the car and the maximum capacity of the tank. Going to say
that longer distances are possible with a lighter frame and a larger tank but this would lead to less
security and overall efficiency.

4.2.5 SUMMARY VEHICLE RANGE

Clearly gasoline and diesel vehicles have the edge on range. Already discussed in the energy storage
section, they are able to store massive amounts of chemical energy on-board providing this range.
The inability to store much energy on-board the compressed air or electric vehicle will unfortunately
cause the “range anxiety” condition already discussed previously. Compressed air and electric
vehicles may be good for tight urban areas or small communities, but will not be widely accepted
where the customer must drive even moderate distances.

4.3 ADVANTAGES AND DISADVANTAGES

4.3.1 COMPRESSED AIR VEHICLE ADVANTAGES AND DISADVANTAGES

ADVANTAGES

The vehicle can be plugged in to a residential electrical outlet and charged at home (11)
The cost of parts and labor to build the vehicle should be lower because there is no cooling
system, spark plugs, starter motor, or mufflers
Since there is no cooling system, one source of vehicle wind drag will be eliminated (the
radiator) and thus reduce the energy to move the vehicle forward
As air expands it cools and this can be utilized for a compressed air vehicle air conditioning
system
The vehicles can be run in harsh environments like mines without the risk of igniting
underground methane buildup because there is no hot exhaust
Reduction and /or elimination of hazardous substances like reactive battery metals, battery
acid and gasoline
The only emission from the vehicle is cold air when the source of the air compressor power
comes from a non-carbon source like nuclear, solar or wind energy
The vehicle truly emits zero emissions at the place where it is operating
Compressed air vehicles are mechanically simpler than gasoline or diesel vehicles, which
make them more reliable.
Some compressed air vehicles can capture energy during braking, increasing range and
efficiency.
The use of compressed air vehicles reduces the dependence on foreign oil.

DISADVANTAGES

The serial efficiency back to the power plant is low, this could place a huge demand on the
power plant should these vehicles become widely excepted



Since the serial efficiency is low, the carbon footprint will be high for countries whose power
plants use predominantly fossil fuels
Although one advantage is no need for an engine cooling system, a disadvantage is in all
likelihood to improve efficiency of a compressed air vehicle a “heating” system or heat
exchange will be needed to input the energy during air expansion that was lost during
compression the storage tank.
A further disadvantages is the heat exchange may become cold and be subject to icing in
cool moist climates
When a compressed air storage tank is filled, heat energy is released. If the energy is not
dissipated the temperature of the tanks will rise.
Charging the compressed air tank will take around 3 hrs when the compressor is powered by
a residential wall plug (11)
Compressed air vehicles will create a condition known as “range anxiety” with customers.
Without a refueling infrastructure, the customer must plan every trip to arrive home before
the compressed air tank dissipates.

4.3.2 BATTERY ELECTRIC VEHICLE COST ADVANTAGES AND DISADVANTAGES

ADVANTAGES

The vehicle can be plugged in to a residential electrical outlet and charged at home.
The vehicle truly emits zero emissions at the place where it is operating.
Electric vehicles are mechanically simpler than gasoline or diesel vehicles, which should
make them more reliable.
Electric vehicles can recapture energy during braking, increasing range and efficiency.
Electric motors produce full torque at zero rpm, leading to smoother acceleration and no
vibration at zero speed.
The use of electric vehicles reduces dependence on foreign oil.

DISADVANTAGES
In cold climates, electric vehicles require resistive heaters for the occupants, reducing range.
The batteries also have reduced capacity in severely cold climates and may require thermal
management systems.
Total energy storage on board an electrical vehicle is roughly equivalent to 1 gallon of gas,
thus limiting range of vehicle.
Electrical vehicles do not emit sounds, thus making the vehicles dangerous to pedestrians.
In the United States, there is little or no infrastructure to charge vehicles away from the
residential neighborhood.
For customers living in apartments, or parking on city streets, there is no infrastructure to
charge their vehicle.
Vehicle charging takes too much time compared to refilling a gasoline vehicle with energy,
roughly 8 hours on a fast charge versus minutes for a gasoline vehicle.
The batteries on-board electric vehicles are toxic, and hazardous in accidents.
Batteries are very expensive, limiting the projected growth of electric vehicles.
Electric vehicles also create a condition known as “range anxiety” with customers. Without
a recharging infrastructure, the customer must plan every trip to arrive home before the
charge dissipates.



4.3.3 GASOLINE VEHICLE COST ADVANTAGES AND DISADVANTAGES

Advantages

Gasoline engines have the ability to produce reasonably large amount of horsepower.
Especially compared to that of electric and compressed air propelled vehicles.
Gasoline engines are very easily tunable. Even the average man can get under the hood of a
gasoline vehicle. The cost of gasoline engine parts is much more inexpensive then any other
system.
Gasoline engines are capable of much greater power levels than that of non-combustion
engines. This can be very appealing for many consumers.
A combustion engine is much less expensive to manufacture per unit of power output.
Gasoline has a high energy density resulting in vehicles having long a long range as shown in
the calculations. (46)

Disadvantages

The world has a finite supply of petroleum, and we consume it at an extremely high rate. An
alternative source will need to be found eventually in time.
Gasoline engines produce more carbon dioxide emissions and other greenhouse gases, such
as nitrogen oxide, than engines using alternative fuel sources.
Gasoline is expensive, with extremely fluctuating prices, spending most of the time on the
rise.

4.3.4 DIESEL VEHICLE COST ADVANTAGES AND DISADVANTAGES

Advantages

Diesel engines get between 20 - 30% more gas mileage than comparable gas-based engines,
meaning that they have a longer range for an equal quantity of gas.
Diesel produces less carbon dioxide emissions than gasoline.
Diesel engines are capable of running on bio-diesel fuel sources without the need for
previous modification.
Diesel engine design is simpler than a gas powered engine and therefore it requires less and
cheaper maintenance.

Disadvantages

Diesel motors are more expensive than gas-based a motor which leads to a higher vehicle
cost.
Diesel fuel creates a larger carbon footprint than gas-based fuel based on well to wheel
analysis.
Diesel costs more than gasoline.
Refilling at truck stops is not preferred by customers.
Diesel motors are noisier than their gas-based counterparts.



5.0 CONCLUSION
Serial efficiency of a compressed air vehicle is very low when calculated from the motor output back
to the energy generation at the power plant. For this reason, 1 unit of energy used at the compressed
air motor equates to 20.5 units of energy used at the power plant. Compare this to only 5.2 units of
energy used at the power plant for electric vehicles. The low serial efficiency is owed predominately
due the low efficiency of the energy conversion process from electricity to compressed air and then
from compressed air to motor power output. This low serial efficiency could place a huge demand
on the electric grid should compressed air vehicles become widely accepted. Although single stage
compression and expansion were utilized for this analysis, one technique currently being used to
improve the conversion efficiency is multiple stage compression and expansion of the air. This will
improve efficiency but will not improve it enough to compete with the serial efficiency of electric
vehicles.

In terms of environmental impact, the compressed air vehicle has zero emission if it is used in areas
that use non carbon emitting power plants like nuclear, solar, hydro or wind power. On the contrary,
using a compressed air vehicle in an area that utilizes a carbon producing power plant makes the
vehicle have a very high CO2 output. In fact, on a per kw-hr basis, the CO2 emission from a
compressed air motor is higher than gasoline, diesel and electric combined. This is owed to a low
serial efficiency of the compression and expansion processes.

From the standpoint of conversion technology cost per kw produced or "bang for buck", pneumatic
motors are high cost. This can be attributed to the relatively low power output of air motors per
motor volumetric piston displacement. Comparing a compressed air motor and a gasoline engine of
the same displacement, the cylinder pressure is much higher for internal combustion and thus the
PV work is much higher giving gasoline a much lower $/kw value. Although the compressed air
motor has less content like fuel injection system, coolant passages and an ignition system the $/kw is
still higher for compressed air due to the low output of the motor.

Comparing compressed air energy storage with other popular energy storage types, compressed air
has 693 times less energy storage capacity per unit volume than gasoline and 23.2 times less than
lithium ion batteries. As a result of this low energy storage capacity the range of the vehicle is limited.
To improve the range of the vehicle, one technique being utilized is reheat of the air as it expands
from the storage tank in order input energy that was lost during isothermal compression. Storage of
a fuel like gasoline on board effectively increases the average total energy density of the fuels
onboard and dramatically increases the range of the vehicle but also increases the carbon emissions.



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