FOR FINAL YEAR EIGHT SEMESTER MECHANICAL ENGINEERING STUDENTS

1. 1
ME 6016
ADVANCED IC
ENGINES
UNIT V
RECENT TRENDS

2. 2
HCCI Engine
Homogeneous charge compression ignition (HCCI) is a form of internal combustion
in which well-mixed fuel and oxidizer (typically air) are compressed to the point of
auto-ignition. As in other forms of combustion, this exothermic reaction releases
chemical energy into a sensible form that can be transformed in an engine into work
and heat.
Introduction
HCCI has characteristics of the two most popular forms of combustion used in SI
engines: homogeneous charge spark ignition (gasoline engines) and CI engines:
stratified charge compression ignition (diesel engines). As in homogeneous charge
spark ignition, the fuel and oxidizer are mixed together. However, rather than using
an electric discharge to ignite a portion of the mixture, the density and temperature
of the mixture are raised by compression until the entire mixture reacts
spontaneously. Stratified charge compression ignition also relies on temperature and
density increase resulting from compression, but combustion occurs at the boundary
of fuel-air mixing, caused by an injection event, to initiate combustion.
The defining characteristic of HCCI is that the ignition occurs at several places at a
time which makes the fuel/air mixture burn nearly simultaneously. There is no direct
initiator of combustion. This makes the process inherently challenging to control.
However, with advances in microprocessors and a physical understanding of the
ignition process, HCCI can be controlled to achieve gasoline engine-like emissions
along with diesel engine-like efficiency. In fact, HCCI engines have been shown to
achieve extremely low levels of Nitrogen oxide emissions (NOx) without an after
treatment catalytic converter. The unburned hydrocarbon and carbon monoxide
emissions are still high (due to lower peak temperatures), as in gasoline engines, and
must still be treated to meet automotive emission regulations.
Recent research has shown that the use of two fuels with different reactivities (such
as gasoline and diesel) can help solve some of the difficulties of controlling HCCI
ignition and burn rates. RCCI or Reactivity Controlled Compression Ignition has
been demonstrated to provide highly efficient, low emissions operation over wide
load and speed ranges *.
HCCI engines have a long history, even though HCCI has not been as widely
implemented as spark ignition or diesel injection. It is essentially an Otto combustion
cycle. In fact, HCCI was popular before electronic spark ignition was used. One
example is the hot-bulb engine which used a hot vaporization chamber to help mix
fuel with air. The extra heat combined with compression induced the conditions for
combustion to occur. Another example is the "diesel" model aircraft engine.

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Operation
Methods
A mixture of fuel and air will ignite when the concentration and temperature of
0reactants is sufficiently high. The concentration and/or temperature can be
increased by several different ways:
 High compression ratio
 Pre-heating of induction gases
 Forced induction
 Retained or re-inducted exhaust gases
Once ignited, combustion occurs very quickly. When auto-ignition occurs too early
or with too much chemical energy, combustion is too fast and high in-cylinder
pressures can destroy an engine. For this reason, HCCI is typically operated at lean
overall fuel mixtures.
Advantages
 HCCI provides up to a 30-percent fuel savings, while meeting current
emissions standards.
 Since HCCI engines are fuel-lean, they can operate at a Diesel-like
compression ratios (>15), thus achieving higher efficiencies than conventional
spark-ignited gasoline engines.
 Homogeneous mixing of fuel and air leads to cleaner combustion and lower
emissions. Actually, because peak temperatures are significantly lower than
in typical spark ignited engines, NOx levels are almost negligible.
Additionally, the premixed lean mixture does not produce soot.

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 HCCI engines can operate on gasoline, diesel fuel, and most alternative fuels.
 In regards to gasoline engines, the omission of throttle losses improves HCCI
efficiency.
Disadvantages
 High in-cylinder peak pressures may cause damage to the engine.
 High heat release and pressure rise rates contribute to engine wear.
 The auto ignition event is difficult to control, unlike the ignition event in
spark ignition (SI) and diesel engines which are controlled by spark plugs and
in-cylinder fuel injectors, respectively.
 HCCI engines have a small power range, constrained at low loads by lean
flammability limits and high loads by in-cylinder pressure restrictions.
 Carbon monoxide (CO) and hydrocarbon (HC) pre-catalyst emissions are
higher than a typical spark ignition engine, caused by incomplete oxidation
(due to the rapid combustion event and low in-cylinder temperatures) and
trapped crevice gases, respectively.
Control
Controlling HCCI is a major hurdle to more widespread commercialization. HCCI is
more difficult to control than other popular modern combustion engines, such as
Spark Ignition (SI) and Diesel. In a typical gasoline engine, a spark is used to ignite
the pre-mixed fuel and air. In Diesel engines, combustion begins when the fuel is
injected into compressed air. In both cases, the timing of combustion is explicitly
controlled. In an HCCI engine, however, the homogeneous mixture of fuel and air is
compressed and combustion begins whenever the appropriate conditions are
reached. This means that there is no well-defined combustion initiator that can be
directly controlled. Engines can be designed so that the ignition conditions occur at a
desirable timing. To achieve dynamic operation in an HCCI engine, the control
system must change the conditions that induce combustion. Thus, the engine must
control either the compression ratio, inducted gas temperature, inducted gas
pressure, fuel-air ratio, or quantity of retained or re-inducted exhaust. Several
control approaches are discussed below.
Variable compression ratio
There are several methods for modulating both the geometric and effective
compression ratio. The geometric compression ratio can be changed with a movable
plunger at the top of the cylinder head. This is the system used in "diesel" model
aircraft engines. The effective compression ratio can be reduced from the geometric

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ratio by closing the intake valve either very late or very early with some form of
variable valve actuation (i.e. variable valve timing permitting Miller cycle). Both of
the approaches mentioned above require some amounts of energy to achieve fast
responses. Additionally, implementation is expensive. Control of an HCCI engine
using variable compression ratio strategies has been shown effective. The effect of
compression ratio on HCCI combustion has also been studied extensively.
Variable induction temperature
In HCCI engines, the autoignition event is highly sensitive to temperature. Various
methods have been developed which use temperature to control combustion timing.
The simplest method uses resistance heaters to vary the inlet temperature, but this
approach is slow (cannot change on a cycle-to-cycle basis). Another technique is
known as fast thermal management (FTM). It is accomplished by rapidly varying the
cycle to cycle intake charge temperature by rapidly mixing hot and cold air streams.
It is also expensive to implement and has limited bandwidth associated with
actuator energy.
Variable exhaust gas percentage
Exhaust gas can be very hot if retained or re-inducted from the previous combustion
cycle or cool if recirculated through the intake as in conventional EGR systems. The
exhaust has dual effects on HCCI combustion. It dilutes the fresh charge, delaying
ignition and reducing the chemical energy and engine work. Hot combustion
products conversely will increase the temperature of the gases in the cylinder and
advance ignition. Control of combustion timing HCCI engines using EGR has been
shown experimentally.
Variable valve actuation
Variable valve actuation (VVA) has been proven to extend the HCCI operating
region by giving finer control over the temperature-pressure-time history within the
combustion chamber. VVA can achieve this via two distinct methods:
 Controlling the effective compression ratio: A variable duration VVA system
on intake can control the point at which the intake valve closes. If this is
retarded past bottom dead center (BDC), then the compression ratio will
change, altering the in-cylinder pressure-time history prior to combustion.
 Controlling the amount of hot exhaust gas retained in the combustion
chamber: A VVA system can be used to control the amount of hot internal
exhaust gas recirculation (EGR) within the combustion chamber. This can be
achieved with several methods, including valve re-opening and changes in
valve overlap. By balancing the percentage of cooled external EGR with the

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hot internal EGR generated by a VVA system, it may be possible to control
the in-cylinder temperature.
While electro-hydraulic and camless VVA systems can be used to give a great deal of
control over the valve event, the componentry for such systems is currently
complicated and expensive. Mechanical variable lift and duration systems, however,
although still being more complex than a standard valvetrain, are far cheaper and
less complicated. If the desired VVA characteristic is known, then it is relatively
simple to configure such systems to achieve the necessary control over the valve lift
curve. Also see variable valve timing.
Variable fuel ignition quality
Another means to extend the operating range is to control the onset of ignition and
the heat release rate is by manipulating fuel itself. This is usually carried out by
adopting multiple fuels and blending them "on the fly" for the same engine .
Examples could be blending of commercial gasoline and diesel fuels , adopting
natural gas or ethanol ". This can be achieved in a number of ways;
 Blending fuels upstream of the engine: Two fuels are mixed in the liquid
phase, one with low resistance to ignition (such as diesel fuel) and a second
with a greater resistance (gasoline), the timing of ignition is controlled by
varying the compositional ratio of these fuels. Fuel is then delivered using
either a port or direct injection event.
 Having two fuel circuits: Fuel A can be injected in the intake duct (port
injection) and Fuel B using a direct injection (in-cylinder) event, the
proportion of these fuels can be used to control ignition, heat release rate as
well as exhaust gas emissions.
Learn burn engines
Principle
A lean burn mode is a way to reduce throttling losses. An engine in a typical vehicle
is sized for providing the power desired for acceleration, but must operate well
below that point in normal steady-speed operation. Ordinarily, the power is cut by
partially closing a throttle. However, the extra work done in pumping air through
the throttle reduces efficiency. If the fuel/air ratio is reduced, then lower power can
be achieved with the throttle closer to fully open, and the efficiency during normal
driving (below the maximum torque capability of the engine) can be higher.

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The engines designed for lean burning can employ higher compression ratios and
thus provide better performance, efficient fuel use and low exhaust hydrocarbon
emissions than those found in conventional petrol engines. Ultra lean mixtures with
very high air-fuel ratios can only be achieved by direct injection engines.
The main drawback of lean burning is that a complex catalytic converter system is
required to reduce NOx emissions. Lean burn engines do not work well with
modern 3-way catalytic converter—which require a pollutant balance at the exhaust
port so they can carry out oxidation and reduction reactions—so most modern
engines run at or near the stoichiometric point. Alternatively, ultra-lean ratios can
reduce NOx emissions.
Heavy-duty gas engines
Lean burn concepts are often used for the design of heavy-duty natural gas, biogas,
and liquefied petroleum gas (LPG) fuelled engines. These engines can either be full-
time lean burn, where the engine runs with a weak air-fuel mixture regardless of
load and engine speed, or part-time lean burn (also known as "lean mix" or "mixed
lean"), where the engine runs lean only during low load and at high engine speeds,
reverting to a stoichiometric air-fuel mixture in other cases.
Heavy-duty lean burn gas engines admit as much as 75% more air than theoretically
needed for complete combustion into the combustion chambers. The extremely weak
air-fuel mixtures lead to lower combustion temperatures and therefore lower NOx
formation. While lean-burn gas engines offer higher theoretical thermal efficiencies,
transient response and performance may be compromised in certain situations. Lean
burn gas engines are almost always turbocharged, resulting high power and torque
figures not achieveable with stoichiometric engines due to high combustion
temperatures.
Heavy duty gas engines may employ precombustion chambers in the cylinder head.
A lean gas and air mixture is first highly compressed in the main chamber by the
piston. A much richer, though much lesser volume gas/air mixture is introduced to
the precombustion chamber and ignited by spark plug. The flame front spreads to
the lean gas air mixture in the cylinder.
This two stage lean burn combustion produces low NOx and no particulate
emissions. Thermal efficiency is better as higher compression ratios are achieved.
Manufacturers of heavy-duty lean burn gas engines include GE Jenbacher, MAN
Diesel & Turbo, Wärtsilä, Mitsubishi Heavy Industries and Rolls-Royce plc.
Honda lean burn systems

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One of the newest lean-burn technologies available in automobiles currently in
production uses very precise control of fuel injection, a strong air-fuel swirl created
in the combustion chamber, a new linear air-fuel sensor (LAF type O2 sensor) and a
lean-burn NOx catalyst to further reduce the resulting NOx emissions that increase
under "lean-burn" conditions and meet NOx emissions requirements.
This stratified-charge approach to lean-burn combustion means that the air-fuel ratio
isn't equal throughout the cylinder. Instead, precise control over fuel injection and
intake flow dynamics allows a greater concentration of fuel closer to the spark plug
tip (richer), which is required for successful ignition and flame spread for complete
combustion. The remainder of the cylinders' intake charge is progressively leaner
with an overall average air:fuel ratio falling into the lean-burn category of up to 22:1.
The older Honda engines that used lean burn (not all did) accomplished this by
having a parallel fuel and intake system that fed a pre-chamber the "ideal" ratio for
initial combustion. This burning mixture was then opened to the main chamber
where a much larger and leaner mix then ignited to provide sufficient power.
During the time this design was in production this system (CVCC, Compound
Vortex Controlled Combustion) primarily allowed lower emissions without the need
for a catalytic converter. These were carbureted engines and the relative "imprecise"
nature of such limited the MPG abilities of the concept that now under MPI (Multi-
Port fuel Injection) allows for higher MPG too.
The newer Honda stratified charge (lean burn engines) operate on air-fuel ratios as
high as 22:1. The amount of fuel drawn into the engine is much lower than a typical
gasoline engine, which operates at 14.7:1—the chemical stoichiometric ideal for
complete combustion when averaging gasoline to the petrochemical industries'
accepted standard of C6H8.
This lean-burn ability by the necessity of the limits of physics, and the chemistry of
combustion as it applies to a current gasoline engine must be limited to light load
and lower RPM conditions. A "top" speed cut-off point is required since leaner
gasoline fuel mixtures burn slower and for power to be produced combustion must
be "complete" by the time the exhaust valve open
Stratified charge engines

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In a stratified charge engine, the fuel is injected into the cylinder just before ignition.
This allows for higher compression ratios without "knock," and leaner air/fuel
mixtures than in conventional internal combustion engines.
Conventionally, a four-stroke (petrol or gasoline) Otto cycle engine is fuelled by
drawing a mixture of air and fuel into the combustion chamber during the intake
stroke. This produces a homogeneous charge: a homogeneous mixture of air and
fuel, which is ignited by a spark plug at a predetermined moment near the top of the
compression stroke.
In a homogeneous charge system, the air/fuel ratio is kept very close to
stoichiometric. A stoichiometric mixture contains the exact amount of air necessary
for a complete combustion of the fuel. This gives stable combustion, but places an
upper limit on the engine's efficiency: any attempt to improve fuel economy by
running a lean mixture with a homogeneous charge results in unstable combustion;
this impacts on power and emissions, notably of nitrogen oxides or NOx.
If the Otto cycle is abandoned, however, and fuel is injected directly into the
combustion-chamber during the compression stroke, the petrol engine is liberated
from a number of its limitations.
First, a higher mechanical compression ratio (or, with supercharged engines,
maximum combustion pressure) may be used for better thermodynamic efficiency.
Since fuel is not present in the combustion chamber until virtually the point at which
combustion is required to begin, there is no risk of pre-ignition or engine knock.
The engine may also run on a much leaner overall air/fuel ratio, using stratified
charge.

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Combustion can be problematic if a lean mixture is present at the spark-plug.
However, fueling a petrol engine directly allows more fuel to be directed towards
the spark-plug than elsewhere in the combustion-chamber. This results in a stratified
charge: one in which the air/fuel ratio is not homogeneous throughout the
combustion-chamber, but varies in a controlled (and potentially quite complex) way
across the volume of the cylinder.
A relatively rich air/fuel mixture is directed to the spark-plug using multi-hole
injectors. This mixture is sparked, giving a strong, even and predictable flame-front.
This in turn results in a high-quality combustion of the much weaker mixture
elsewhere in the cylinder.
Direct fuelling of petrol engines is rapidly becoming the norm, as it offers
considerable advantages over port-fuelling (in which the fuel injectors are placed in
the intake ports, giving homogeneous charge), with no real drawbacks. Powerful
electronic management systems mean that there is not even a significant cost
penalty.
With the further impetus of tightening emissions legislation, the motor industry in
Europe and north America has now switched completely to direct fuelling for the
new petrol engines it is introducing.
It is worth comparing contemporary directly-fuelled petrol engines with direct-
injection diesels. Petrol can burn faster than diesel fuel, allowing higher maximum
engine speeds and thus greater maximum power for sporting engines. Diesel fuel,
on the other hand, has a higher energy density, and in combination with higher
combustion pressures can deliver very strong torque and high thermodynamic
efficiency for more 'normal' road vehicles.
Four-valve engines
‡ A 4-Valve engine is designed for better performance than a regular 2-Valve
engine
‡ More power: The 4-valve provides for a greater intake and exhaust area
resulting inmore power.
More Mileage: 4-valve not only enhances the performance but also returns a
very good fuel economy
More green: Comfortably meets BSIII regulations
What is the 4-valve engine?
‡ An engine that has valves that let the air-fuel mixture into the combustion
chamber to be burned and then draw out the exhaust gas after the combustion.
A conventional engine has one intake valve to let in the air-fuel mixture and

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one exhaust valve to let out the exhaust gases. But the 4-valve engine has
two intake and two exhaust valves.
A typical 2-valve engine has just 1/3 combustion chamber head area covered by
the valves, but a 4-valve head increases that to more than 50%, hence smoother
and quicker breathing. 4-valve design also benefits from a clean and effective
combustion, because the spark plug can be placed in the middle. 4 valves are
better to be driven by twin-cam, one for intake valves and one for exhaust
valves.4-valve type and its shape is designed with the minimum area necessary
for the two intake and two exhaust valves. At the same time it is designed with
a minimum intake and exhaust valve angles to realize an optimum combustion
chamber shape.
M E RITS:-
‡ The first merit of 4-valve design is that it allows the sparkplug to be positioned
in the center of the combustion chamber to provide more efficient flame spread
and combustion. In other words, it enables highly efficientcombustion. Also,
the 4-valve design enables greater overall valve area than a 2-valve system for
more efficient (per unit of area) intake and exhaust function. This is the second
major merit.
COMPARISION OF 4-VALVES OVER 2-VALVES
‡ A conventional engine has one intake valve to let in the air-fuel mixture and
one exhaust valve to let out the exhaust gases. But the 4-valve engine has two
intake and two exhaust valves 4-valves is better than two because 4-valves give
an engine steadier low-speed performance and a better acceleration
feeling.That is why most race engines and high-performance engines have four
valves.
For example, Yamaha¶s YZR-M1 MotoGP race machine has four valves.
The name of the game is velocity and turbulence/mixing of the intake charge
at differing engine speeds. At low engine speeds, one intake valve gives
increased velocity, hence better gas mixing and better cylinder filling. If you
open a second intake valve at low engine speed, the velocity drops
dramatically, leaving poor intake filling and a lean intake charge. The result
is engine knock and less torque. On the other hand, at high RPM, breathing
is the name of the game. The valves are open such a short length of time
you need the maximum available intake area. Therefore 2 intake valves
work better at high RPM. All of this is of course subject to the exhaust
system design. A proper extractor exhaust can make a significant difference
on a two valve system and a restrictive exhaust can nullify all the gains of a
4 valve system.
‡ When you have only 2 valves, the air/fuel mixture entering the cylinder can
be tangential to the circle of the cylinder, giving a high degree of swirl, better
air/fuel mixing and hence better performance at lower revs in an SI engine.

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At higher revs, enough turbulence is available to create good mixing, and so
4 valves are better, as they allow greater airflow.
OHV engine design
OHV means OverHead Valve - an engine
design where the camshaft is installed inside
the engine block and valves are operated
through lifters, pushrods and rocker arms (an
OHV engine also known as a "Pushrod"
engine). Although an OHV design is a bit
outdated, it has been successfully used for
decades. An OHV engine is very simple, it has
more compact size and proven to be durable.
On the downside, it's difficult to precisely
control the valve timing at high rpm due to
higher inertia caused by larger amount of valve train components (lifter-pushrod-
rocker arm). Also, it's very difficult to install more than 2 valves per cylinder, or
implement some of the latest technologies such as Variable Valve Timing -
something that could be easily done in a DOHC engine.
4-cylinder inline 8-valve OHV engine

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OHC or SOHC engine
OHC in general means OverHead Cam while
SOHC means Single OverHead Cam.
In a SOHC engine the camshaft is installed in
the cylinder head and valves are operated
either by the rocker arms or directly through
the lifters (as in the picture).
The advantage is that valves are operated
almost directly by the camshaft, which makes it
easy to achieve the perfect timing at high rpm.
It's also possible to install three or four valves
per cylinder
The disadvantage is that an OHC engine
requires a timing belt or chain with related components, which is more complex and
more expensive design.
4-cylinder 8-valve SOHC engine
DOHC or Twin Cam engine
4-cylinder 16-valve DOHC engine
DOHC means Double OverHead Cam, or
sometimes it could be called "Twin Cam". A
DOHC setup is used in most of newer cars. Since
it's possible to install multiple valves per
cylinder and place intake valves on the opposite
side from exhaust vales, a DOHC engine can
"breathe" better, meaning that it can produce
more horsepower with smaller engine volume.
Compare: The 3.5-liter V6 DOHC engine of 2003
Nissan Pathfinder has 240 hp, similar to 245 hp
of the 5.9-liter V8 OHV engine of 2003 Dodge
Durango.
Pros: High efficiency, possible to install multiple
valves per cylinder and adopt variable timing.
Cons: More complex and more expensive
design.
Electronic Engine Management

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Electronic control systems
Engines are subject to very high stresses during compression and ignition, and
increasingly stringent emission standards have made better control of the diesel
combustion process necessary.
Electronic controlled diesel systems give very precise control of the fuel injection
and combustion process. Electronic controls have delivered other benefits besides a
reduction in fuel consumption and emissions, such as an increase in power and
torque; improved engine responsiveness; a reduction in engine noise and diesel
knock; and improved and expanded diagnostic capabilities through the use of scan
tools.
Electronic control systems monitor and control many variables, including:
 Engine speed:
o to maintain a smooth functional idle,
o and to limit the maximum safe engine speed, power, and torque;
o and to keep the engine output to within safe limits.
 Fuel injector operation:
o including the timing, rate and volume of fuel injected.
 Glow plugs and heater elements:
o Control of pre-heating of the intake air to support quick cold starting
and reduced cold run emissions.
 Exhaust emissions:
o Analysis of exhaust gas to determine combustion efficiency and
pollutants.
 And the data bus:
o An electronic communications network that allows exchange of data
between computers - necessary for efficient operation and fault
diagnosis.
Other inputs monitored include:

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 crankshaft position,
 throttle position,
 brake and clutch operation,
 battery voltage,
 cruise control request,
 air, oil fuel, exhaust and coolant temperatures,
 and intake air, oil and fuel pressures.
The ECU is a micro-computer. It is constructed from printed circuitry, and
contains a large number of electrical components, including many
semiconductor devices.
Its input devices receive data as electrical signals. They come from sensors and
components at various locations around the engine. Its processing unit compares
incoming data with data stored in a memory unit. The memory unit contains basic
data about how the engine is to operate. And an output device pulses the
electrical circuit of the solenoid-type injection valves.
It is normally located in a safe place, behind a kick-panel in the foot-well, under
the passenger seat, or in the boot, and connected by a multi-plug, or plugs, to the
vehicle’s wiring harness.
The core function of a basic ECU in an EFI system is to control the pulse width of
the injector. More sophisticated models also control other functions such as idle
speed, ignition timing, and the fuel pump. These wider systems are called engine
management systems. The more precise control they allow is very effective in
reducing fuel consumption and exhaust emissions.
The ECU adjusts quickly to changing conditions by using what are called
programmed characteristic maps, stored in the memory unit. They are
programmed into the ECU, just as data is programmed into a computer.
Characteristics means the engine’s operating conditions. And they are called maps
because they map all of the operating conditions for the engine.
They are constructed first from dynamometer tests, then fine-tuned, to optimise
the operating conditions and to comply with emission regulations. This data is
stored electronically.
Ignition timing is crucial in this process. Between one spark and the next, the ECU
uses data it receives on engine load and speed to determine when the next
ignition point will occur. It can also correct the map value, using extra information
such as engine coolant temperature, intake air temperature, or throttle position.

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Putting all of this together, it arrives at the best ignition point for that operating
condition.
Common Rail Direct Injection or CRDI
CRDI is an intelligent way of controlling a diesel engine with use of modern
computer systems. CRDI helps to improve the power, performance and reduce
harmful emissions from a diesel engine. Conventional Diesel Engines (non-CRDI
engines) are sluggish, noisy and poor in performance compared to a CRDI engine.
CRDI or common rail direct injection system is also sometimes referred to by many
similar or different names. Some brands use name CRDe / DICOR / Turbojet / DDIS /
TDI etc. All these systems work on same principles with slight variations and
enhancements here and there.
CRDI system uses common rail which is like one single rail or fuel channel which
contains diesel compresses at high pressure. This is a called a common rail because
there is one single pump which compresses the diesel and one single rail which
contains that compressed fuel. In conventional diesel engines, there will be as many
pumps and fuel rails as there are cylinders.
As an example, for a conventional 4 cylinder diesel engine there will be 4 fuel-
pumps, 4 fuel rails each feeding to one cylinder. In CRDI, there will be one fuel rail
for all 4 cylinders so that the fuel for all the cylinders is pressurized at same
pressure.
The fuel is injected into each engine cylinder at a particular time interval based on
the position of moving piston inside the cylinder. In a conventional non-CRDI
system, this interval and the fuel quantity was determined by mechanical
components, but in a CRDI system this time interval and timing etc are all controlled
by a central computer or microprocessor based control system.

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To run a CRDI system, the microprocessor works with input from multiple sensors.
Based on the input from these sensors, the microprocessor can calculate the precise
amount of the diesel and the timing when the diesel should be injected inside the
cylinder. Using these calculations, the CRDI control system delivers the right
amount of diesel at the right time to allow best possible output with least emissions
and least possible wastage of fuel.
The input sensors include throttle position sensor, crank position sensor, pressure
sensor, lambda sensor etc. The use of sensors and microprocessor to control the
engine makes most efficient use of the fuel and also improved the power, fuel-
economy and performance of the engine by managing it in a much better way.
One more major difference between a CRDI and conventional diesel engine is the
way the fuel Injectors are controlled. In case of a conventional Engine, the fuel
injectors are controlled by mechanical components to operate the fuel injectors. Use
of these mechanical components adds additional noise as there are many moving
components in the injector mechanism of a conventional diesel engine. In case of a
CRDI engine, the fuel injectors are operated using solenoid valves which operate on
electric current and do not require complex and noisy mechanical arrangement to
operate the fuel Injection into the cylinder. The solenoid valves are operated by the
central microprocessor of the CRDI control system based on the inputs from the
sensors used in the system.

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Gasoline Direct Injection Engine :
Port fuel injected (PFI) engines are the most commonly used spark ignition (SI)
engine in current vehicles. In certain markets, a very small number of direct-injected
spark ignition (DISI) engines have been introduced. Both use gasoline fuel. In
PFI engines, fuel is injected into the intake port near the closed intake valve,
producing a well mixed fuel–air charge in the combustion chamber. This is the most
commonly used engine type in current vehicles. These engines are typically operated
with a stoichiometric fuel–air ratio, which is the ratio that permits complete
conversion of the fuel and oxygen in the intake charge to form CO2 and H2O. As a
result of the premixed combustion, it produces very low particulate emissions.
The levels of other emissions directly leaving the engine are relatively high, and
compliance with regulated emission standards relies on the effectiveness of the
three-way catalyst, which reduces emissions by 95–99% as discussed in more detail
below.
In DISI engines, the fuel is injected directly into the combustion chamber. At higher
load, the fuel is injected during the intake stroke to form a nearly homogeneous fuel–
air mixture at the time of ignition. At lower load, the injection timing can be delayed
until the compression stroke to produce a ‘‘stratified’’ fuel mixture. This mixture is
ideally uniform,premixed, and stoichiometric near the center, and devoid of
fuel near the cylinder walls. This spatial localization translates into a faster burn and
allows the engine to be run more fuel lean overall than PFI engines, providing
improved fuel economy and better performance during transient acceleration/
deceleration. In practice, however, it is difficult to realize this idealized mixing, and
fuel-rich and lean regions result,leading to reduced benefits. Additionally, because
this engine injects fuel droplets directly into the combustion chamber,particulate
emissions are increased substantially relative to PFI engines. Like PFI engines, DISI
engines rely on catalytic devices to significantly reduce engine-out concentrations of
regulated emissions.
1. The engines use injectors that can spray fuel directly into the cylinder during
the compression stroke, along with an extremely high pressure fuel pump
(2,000 PSI). Before GDI, it was far more common to use port fuel injection,
where the injector sprayed fuel at low pressure into the intake manifold.
2. The direct injection process allows the fuel to evaporate in the cylinder and
cool the air/fuel mixture. That helps avoid premature ignition, so…
3. These engines can increase the compression ratio. The Mazda engine goes to a
14:1 ratio, which has never been seen before in a production gasoline engine.
The normal high is 12:1 or so, and that would require premium fuel.
4. Many of the engines are using multiple injector sprays per stroke. One spray
occurs as the air starts flowing in on the intake stroke. The second occurs right
before the spark plug fires. This creates a stratified charge of fuel for a better
burn pattern.

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the advantages of higher compression ratios ,The higher the compression ratio,
the more closely packed the molecules of fuel and air are when the mixture is
ignited by the sparkplug, this causes a more powerful explosion by making a
more violent reaction which produces more power. Higher compression makes
the expansion ratio of the exploding hot gas greater which means that more
energy is impinged on the piston top, pushing it down harder, making more
power. Increasing the compression ratio improves the thermal efficiency of an
engine and this is the primary reason why higher compression increases power.
Improving thermal efficiency improves fuel economy from getting more power
from the same amount of fuel and a reduction of combustion chamber surface
area to volume. This means less wasted combustion heat and more expansion
being used to drive the piston down.