This document discusses internal combustion engines (ICEs) and their energy efficiency, input/output flows, emissions control, and methods for optimizing engine control. It covers topics like typical energy losses in ICE vehicles, the energy content of common fuels, exhaust gas composition and pollutant emissions, European emission standards, ways to mitigate pollutants like optimizing the air/fuel ratio and catalytic converter operation, and guidelines for optimal engine control through sensors and actuators. Tables and diagrams are provided to illustrate concepts like energy distribution, air/fuel ratios, and catalytic converter function.

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SistemasAutomóveis
ICE: energy efficiency,
input/output flow and emissions
control
Mário Alves (mjf@isep.ipp.pt)

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SistemasAutomóveis
Outline
• Energy efficiency in ICE vehicles
• Energy contained in common fuel types
• Input/output flow
• Exhaust gases and pollutant emissions
• European emission standards
• Pollutant emissions mitigation methods
• Air/fuel ratio
• Catalytic converter operation
• Guidelines for optimal engine control

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ICE: energy efficiency
• Energy losses distribution for a typical ICE road vehicle
http://energy.gov/eere/vehicles/fact-880-july-6-2015-conventional-vehicle-energy-use-where-
does-energy-go

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ICE: energy efficiency
• Energy losses distribution for typical ICE road vehicle [1]
[1] http://energy.gov/eere/vehicles/fact-880-july-6-2015-conventional-vehicle-energy-use-where-
does-energy-go

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ICE: energy efficiency
• Energy losses distribution for typical ICE road vehicle [1]
Types of Losses
Types of Driving
Combined City Highway
Engine Losses 68-72% 71-75% 64-69%
Thermal - radiator, exhaust heat, etc. 58-62% 60-64% 56-60%
Combustion 3% 3% 3%
Pumping 4% 5% 3%
Friction 3% 3% 3%
Parasitic Losses
(water & oil pumps, alternator, A/C,
synchroning belt, turbocharger)
4-6% 5-7% 3-4%
Power to Wheels
dissipated as:
18-25% 14-20% 22-30%
Wind Resistance 9-12% 3-5% 13-19%
Rolling Resistance 5-7% 3-5% 6-9%
Braking 5-7% 7-10% 2-3%
Drivetrain Losses 5-6% 4-5% 4-7%
Idle Losses 3% 6% 0%
[1] http://energy.gov/eere/vehicles/fact-880-july-6-2015-conventional-vehicle-energy-use-where-
does-energy-go

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ICE: energy efficiency
[2] http://www.nature.com/nature/journal/v488/n7411/fig_tab/nature11475_F2.html
• Energy losses distribution for a conventional vehicle [2]

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Energy contained in common fuel types
http://greenecon.net/hostage-to-oil/energy_economics.html
kJ/g
kWh/gallon
1 gallon  3,78 litres

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ICE: input/output flow
• Basic input/output flow of an ICE
• Input: air + fuel
• Output: mechanical power + heat + exhaust gases
http://www.ngkntk.co.uk/index.php/technical-centre/lambda-sensors/what-does-the-lambda-
sensor-do/

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ICE: exhaust gases and pollutant emissions
• Fossil fuel is a mixture of hydrocarbons
• ideal combustion process = producing only carbon dioxide (CO2) and
water vapor (H2O).
• exhaust gases are primarily composed of CO2+ H2O + unused engine
charge air
• volume ratios (changes with engine load/conditions):
• CO2 – 2-12%
• H2O – 2-12%
• O2 – 3-17%
• N2 – 60-90%
• Pollutants – 0-1%
https://www.dieselnet.com/tech/emi_intro.php#unreg

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ICE: exhaust gases and pollutant emissions
• Gasoline (left) vs. Diesel (right)
https://www.ngk.de/en/technology-in-detail/lambda-sensors/basic-exhaust-
principles/exhaust-and-harmful-emissions/

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ICE: exhaust gases and pollutant emissions
• Main exhaust gases are innocuous to health/environment
• except for CO2 due to its greenhouse gas properties
• Pollutant emissions:
• unburned hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides
(NOx) and particulate matter (PM)
• affect human health and/or environment
• originate from various non-ideal processes during combustion:
• incomplete combustion of fuel
• reactions between mixture components under high temperature and
pressure
• combustion of engine lubricating oil and oil additives
• combustion of non-hydrocarbon components of diesel fuel, such as
sulfur compounds and fuel additives
https://www.dieselnet.com/tech/emi_intro.php#unreg

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ICE: European emission standards
https://www.ngk.de/en/technology-in-detail/lambda-sensors/basic-exhaust-principles/euro-standards/

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ICE: European emission standards
http://www.vdik.de/department/environment/european-exhaust-gas-emission-standards.html

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ICE: emissions mitigation
• Ways to mitigate pollutant emissions:
• optimizing fuel’s chemical properties
• optimizing ICE design for energy efficiency & emissions
mitigation (e.g. fuel consumption, adaptive cylinder mngmt)
• optimizing ICE operation (e.g. air/fuel ratio, fuel rail pressure,
fuel injection, EGR)
• using/optimizing catalyst converters & particle matter filters
• Air/fuel ratio (lambda factor) is paramount
• for proper ICE operation
• to maximize power
• to minimize fuel consumption
• to minimize pollutant emissions
http://www.pelicanparts.com/techarticles/mult_air_fuel_monitor/FIG2.JPG

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ICE: air/fuel ratio
• “Ideal” air/fuel ratio = stoichiometric ratio
• mass ratio = 14,7 kg (air) : 1 kg (fuel)
• optimizes catalyst operation (minimizes emissions)
• maximizes air/fuel combustion (and thus power)
• minimizes fuel consumption
• Usually expressed as
lambda () factor
•  =
𝑠𝑢𝑝𝑝𝑙𝑖𝑒𝑑 𝑎𝑖𝑟 𝑚𝑎𝑠𝑠
𝑖𝑑𝑒𝑎𝑙 𝑎𝑖𝑟 𝑚𝑎𝑠𝑠
•  = 1  ideal mixture (stoichiometric)
•  > 1 lean mixture
•  < 1 rich mixture
http://www.pelicanparts.com/techarticles/mult_air_fuel_monitor/FIG2.JPG

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ICE: air/fuel ratio
• Air-Fuel ratio changes with engine conditions    1
• cold engine (rich)
• acceleration (rich)
• high altitudes (lean)
• fuel cut-off (lean)
http://www.mummbrothers.com/SRF_Stuff/Secrets/Driveline/Air_Fuel.htm

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ICE: air/fuel ratio
• The air/fuel ratio has a great impact in pollutant emissions
• stoichiometric ratio of 14.7:1 leads to a good compromise
between power, economy and emissions (with catalyzer)
http://www.endtuning.com/afr.html

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ICE: catalytic converter efficiency
• Catalytic converter filtering efficiency
• close to 100% filtering for  = 1 (stoichiometric)
http://www.crypton.co.za/Tto%20know/Emissions/catalitic_converters.html

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ICE: catalytic converter and lambda sensor operation
• 3-way (catalytic converter) = 3 tasks
1. Reduction of nitrogen oxides to nitrogen and oxygen: 2NOx → xO2 + N2
2. Oxidation of carbon monoxide to carbon dioxide: 2CO + O2 → 2CO2
3. Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water:
[NOx] + [CO, HC] → N2 + CO2 + H2O
http://www.crypton.co.za/Tto%20know/Emissions/catalitic_converters.html
ECU basic algorithm (closed-loop, real-time)
1. oxygen (or lambda) sensor gives air/fuel ratio to ECU
2. ECU computes optimal control parameters (injection timing/duration,…)
3. secondary oxygen sensor enables to check catalytic converter failures

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ICE: guidelines for optimal engine control
• For optimized operation, it is mandatory for the engine ECU
to:
• monitor all relevant physical quantities, e.g.:
• intake air pressure (depression)
• crankshaft rotational speed (RPM) and position (angular)
• engine (coolant) and intake air temperature
• throttle position (angular)
• vibration (knock)
• …
• control (closed-loop real-time) all relevant systems, e.g.:
• air/fuel ratio: injection timing + fuel quantity + intake air flow
• ignition timing (SI engines)
• exhaust gas recirculation (EGR)
• adaptive intake/exhaust valve timing control
• adaptive cylinders activation/deactivation
• pre-heating systems (glow plugs in CI, oxygen sensors)
• …

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ICE: a snapshot of ICE control
• A typical ICE control diagram
• notice arrow directions at
the ECU
•  ECU = sensors
•  ECU = actuators
http://enginepartsdiagram.com/1994-toyota-pickup-electronic-
fuel-injection-system-efi-diagram/

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Tips for saving fuel
• Do not warm up at idle – drive immediately after starting the engine
• Always drive in the highest possible gear
• Be light with the accelerator pedal 
• Do not overspeed – fuel consumption increases disproportionately high over 100
km/h (due to drag force and more frequent braking/acceleration)
• Keep enough distance from the vehicle ahead; this improves safety and enables
smoother braking/acceleration
• Release the accelerator pedal when travelling downwards (do not use the neutral
position); this allows engine-assisted braking and cutting-off injection.
• Switch off the engine both at metro/railway crossings and whenever you predict
longer wait times at traffic lights; you begin saving fuel after just 30 seconds
• Avoid superfluous cargo, rooftop equipment or mechanical loads (such as air
conditioning, defoggers)
• Regularly check tire pressure; use recommended pressure for predicted load
• Use synthetic engine oil and low-rolling-resistance tires
• Regularly check glow/ignition plugs and fuel injection

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Glossary (English/Portuguese)

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Recommended bibliography