Combustion Technology in Automobile

 Modern Combustion Technology in Automobile


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
  • 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.
Subsystems Required to Control Low Temperature Combustion Engines ...

  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 

Smoke generated fro the diesel car due to incomplete burning


  • Due to the collection of unburned (hydrocarbon) particles in the exhaust pipe mixes with the surrounding air. This can lead to backfires in bikes

Royal Enfield Swagman silencer - King Indian - YouTube


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 from IC Engine combustion

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

SCR system to control Emissions

  • 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


IC Engine for Low emission bike, BS 6

  • 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

Modern car with Engine exhaust system


  • The engine exhaust system of the car is shown below

  • The catalytic converter for the engine exhaust system 


What are the benefits or drawbacks of the BS6 vehicles or engine ...

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


Swirl and Tumble flow in IC Engine combustion


  • ATFT technology is used by Hero motors 
    • ATFT combustion Technology 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




Leave a Comment