Table of Contents
Modern Combustion Technology in Automobile
by
Dr. Sharad Pachpute
Introduction to Combustion in Automobile
- Basic of combustion would help to understand the working principle of IC engines and pollution controlling technology. The following subjects are essential to understand IC engine combustion
- Thermodynamics
- IC working Principle
- Basic combustion, pollution controls, and techniques to reduce emissions
- CFD modeling of combustion to predict emission
- Internal combustion (IC) engines are widely used in automobiles and machines for power generation
- The power is generated by the combustion of air and fuel in the engine cylinder. The high pressure and temperature gas push the cylinder and the power is transferred to the wheel through a transmission system.
- Combustion of a fuel occurs with air (oxygen) in a small combustion chamber
- The combustion energy is used to drive vehicles using the power transmission systems



- Four-stroke engines are used due to low fuel consumption
- Intake (Suction) Stroke: Air and fuel mixture is inducted inside the cylinder
- Compression stroke: air and fuel mixture is compressed in the cylinder
- Expansion (Power) stroke: after ignition, the combustion produces high-pressure gases to push the piston
- Exhaust stroke: Flue gases are exhausted from the cylinder
- For, a petrol engine, air, and fuel are mixed before combustion and the type of combustion is premixed. A spark plug is used to ignite the mixture.
- However, for diesel engines, the type of combustion is non-premixed. The temperature of the air inside the cylinder is enough high due to compression and fuel-injected fuel burns without any external ignition source
- For homogenized charge compression ignition (HCCI) the type of combustion is partially premixed. The temperature of air and fuel mixture increases due to compression and the mixture burns without any external ignition source.

Combustion in Conventional Engines
Air and Fuel Mixing Mechanism in Petrol Engine
- In a traditional petrol engine, the carburetor has been widely used for mixing of petrol and air
- With the help of a Floating valve, the petrol is injected in the venturi (smallest cross-section) of air dict
- The premixed mixture of air and fuel can be controlled by the throttle valve


- Mixing of air and fuel in the carburetor is due to the venturi effect
Combustion in Petrol Engine
- In petrol engines, air and fuel are mixed prior to combustion. It can be treated as premixed combustion
- The spark plug provides the ignition energy to burn the air and fuel mixture
- Flue gases from the combustion are exhausted
- These flue gases are passed through different post-combustion treatments in order to reduce the emissions such as NOx, SOx etc
Conventional Diesel (Compression Ignition) Engines
- For a diesel engine, fuel is injected over the heated air inside the cylinder
- Liquid fuel injected fuel burns without any additional ignition source
Issues in Conventional Combustion
- Pollution, noise, and discomfort are major issues observed in conventional combustion in IC engines
- Lack of filter to collect the particulate matters
- Major reasons are incomplete mixing of fuel, lack of sufficient time of combustion, and high temperature of flue gases
- Due to the collection of unburned (hydrocarbon) particles in the exhaust pipe mixes with the surrounding air. This can lead to backfires in bikes
Emissions from Engines in Automobile
- There are various types of emissions from petrol and diesel engines such as unburnt hydrocarbon, carbon monoxide, NO and SO
- These emissions can result in the formation of smog in the atmosphere
- It is essential to control or minimize unwanted emissions by adapting fuel-efficient and eco-friendly combustion technologies
Emissions levels for BS4 and BS6
- Emission levels are defined as Pollution Emission Norms by the government of India
- With an increase in an environmental adverse effect, the emission level of all harmful gases have been reduced
- To reduce the emissions, combustion and exhaust systems of IC engines have been modified as per the type of combustion (SI or CI) and fuels
- As per the following table, the emission levels are decreased from BS4 to BS6 engines.
- For both petrol and diesel engines, the NOx level is drastically reduced
- Particulate matter and unburnt hydrocarbon emissions are reduced in BS6 engines


Emission Controls in Automobile
- Noways, various mechanisms have been deployed with combustion chambers in order to reduce emissions such as programmer controlled fuel injectors, exhaust emission reduction using the selective catalytic converter, and particulate traps
- The NOx formed in the IC engine is allowed to pass through a selective catalytic reduction
- The SCR unit is placed in the exhaust duct before the silencer. This is commonly used in most BS-VI bikes
- The amount of ammonia or urea injection into the SCR unit depends on the level of NOx formation
- For the four-wheeler, the SCR unit and muffler are also placed in the exhaust duct before the silencer to reduce particulate matter (PM) and emissions.
- To provide an accurate air-fuel mixture ratio, many modern combustion control techniques have been implemented in many cars and trucks such as MPFI, CRDI, CRDI VCR, GDI, etc. These methods ensure fuel-efficient combustion.
- Exhaust systems are significantly modified with EGR (exhaust gas recirculation), Advanced catalytic converters, SCR( selective catalyst reduction), Urea after-treatment devices, and particulate filters
- The engine exhaust system of the car is shown below
- The catalytic converter for the engine exhaust system
Common Modifications in BS-VI Engines
- The following parts have been improved or added for complete combustion of hydrocarbon, reduction of NOx and particulate matters
- Programmable Fuel Injection System
- Catalytic converter
- Exhaust Gas Re-circulation (EGR)
- Misfire detection unit
- Oxygen sensor at the exhaust
- PM capture unit
Modification in Petrol Engine
- Improved the combustion process (by fuel injection or twin spark plug )
- Better combustion fuel efficiency
- Introduction of EFI instead of a carburetor
- Better fuel quality (higher octane number).
Diesel Engines
- Modification in the exhaust system
- Introduction of diesel particulate filter (DPF) in order to reduce the soot emitted from diesel engines.
- Reduction of the Sulfur content in the exhaust makes more cleaner
- SCR (Selective Catalytic Reduction) in the exhaust system to reduce NOx level
Modern Combustion Systems in Bikes
Digital Twin Spark ignition (DTSi) in Bajaj Bikes
- This technology is widely in Bajaj motorcycles in India
- Digital double spark ignition technology uses two spark plugs on the cylinder
- DTSI technology increases combustion rate due to two spark plugs located around the cylinder
- This method helps the engine to combust fuel at a double rate than normal combustion rate
- This DTSI technology provides in smoother operation of the engine
- TS-Si (Digital Twin Spark Swirl Induction) Technology is developed by Bajaj Automakers. It helps to create swirling motion for fast and better mixing of air and fuel mixture. That results in quick flame propagation and faster combustion
Ignition Technology by Hero Motors
APDV (Advance pro series digital variable) Ignition System
- This technology is developed using electronic combustion and digitally controlled spark plug for a 100 cc motorcycle
- This is an electronically controlled ignition system
- The APDV ignition system provides improved combustion for better mileage and superior engine performance for 100 CC engine
- This technique controls the ignition time digitally using the digital CDI unit and TCI system
Advanced Swirl Flow Induction System (ASFS)
- This technology is developed by Hero Motors Inc. for 125 to 160 cc motorcycle
- It is used for better mixing of air and fuel by creating a swirling motion of inlet charge
Advanced Tumble Flow Induction Technology (ATFI)
- This is also called an improved version of ASFS technology developed by Hero Motors Inc.
- It is developed for improving combustion of mixture
- ATFT technology is used by Hero motors
I3S Technology (Idle Start-Stop System)
- This technology is developed to improve the mileage of their bikes
- Suitable for all the lower cc ( 80 -100 cc) motorcycles
Honda Eco Technology (HET) in IC Engine
- This is for increasing fuel efficiency and boosting up the fuel economy
- This method is similar to Blue core technology (BCT) of Yamaha with some minor modifications
- It is used for reducing friction and improving combustion and optimizing power transmission.
Homogeneous Charge Compression Ignition (HCCI) Technology
- In this technology well-mixed, fuel and air are compressed to the point of auto-ignition. HCCI engine injects the fuel during the intake stroke for combustion
- Instead of electric discharge (spark) to ignite the air-fuel mixture, the compression of the mixture increases the density and temperature up to ignition temperature
- The HCCI is called as low-temperature ignition as the temperature of flue gases is lower ( < 1900 °C)
- HCCI engines result in low levels of NOx emissions without a catalytic converter
- However, the unburned hydrocarbon and carbon monoxide emissions need treatment to meet automotive emission regulations.
- The following figure show, the equivalent ratio (fuel composition) used in the HCCI engine
- Schematic representation of combustion of SI, CI, and HCCI engines



- Petrol (gasoline) engines are clear but less fuel-efficient. Diesel engine combustion is fuel-efficient but more soot particles are emitted. Compared to both engines, the HCCI Engine combustion is more fuel-efficient and emissions are more cleaner compared to SI and CI engine combustion due to good mixing of fuel and air
Modern Fuel Injection Systems in Diesel Engine
- For fuel-efficient combustion and fewer emissions, an electronically controlled unit (ECU) is used nowadays
ECU for Diesel Engine
- Fuel injection into the diesel engine is controlled by ECU as per requirement power generated by the engine
- The command to the fuel injector is passed through the EDU
Dual Fuel ECU for Diesel Engine
- Nowadays, diesel fuel is coupled with gases fuel to get better mileage using the same engine
- Hence, injectors are provided separately for diesel and gases fuels. These injectors are controlled by OEM ECU and diesel control ECU
ECU and EGR for Diesel Engine
- Exhaust gas recirculation (EGR) is used in engines to control emissions by reducing excess oxygen which is responsible for the formation of NOx at high temperature
- ECU and EGR units are provided in modern diesel engines
Scope of CFD Modelings for Pollution from IC Engine
- Numerical models for IC engines have been developed for both premixed and non-premixed combustion
- Computational fluid dynamics (CFD) simulations help to predict emissions generated from petrol and diesel engines with various fuel compositions
- IC ENgine modules are available in ANSYS FLUENT and Star ccm
- CFD Modeling of pollutants like NOx and SOx from IC engines can be carried out to optimize the performance of IC engines
- Different turbulent mixing techniques have been developed by various automobile industries using modeling and testing
- Click here: CFD Modeling of IC Engineers using Ansys FLUENT, Open FOAM, and Star -CCM
Reference
- Bilousov, Ievgen, Bulgakov, Mykola, Savchuk, Volodymyr, Modern Marine Internal Combustion Engines, A Technical and Historical Overview, Springer (2020)
- KTH EGR Diesel Engine , Thesis
- A.K. Agarwal, Fundamental of IC Enignes, IIT Kanpur