Combustion Technologies in IC Engines and Its CFD Modelling

Introduction to IC Engine Combustion

  • Internal combustion (IC) engines are widely used in automobiles  and machines for power generation given in the post
  • The power is generated by the combustion of air and fuel in the engine cylinder.
  • The high pressure and temperature gas pushes 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, 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 engine, the type of combustion is non-premixed. The temperature of 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 mixture burns without any external ignition source.
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Premixed Combustion

  • In a traditional petrol engine, a carburetor has been widely used for mixing of petrol and air
  • With the help of 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 throttle valve
 
  Diesel  Engine Combustion
  • Diesel engine combustion refers to the process by which diesel fuel is burned within the engine to generate power.
  • Unlike gasoline engines, diesel engines rely on compression ignition, where air in the combustion chamber is compressed to a high temperature, causing diesel fuel injected into the chamber to ignite spontaneously.
  • Here’s an overview of the combustion process in a diesel engine:
  1. Air Intake:
    • The diesel engine draws in air through the intake system. Unlike gasoline engines, which use a throttle to control airflow, diesel engines typically have no throttle or use a variable geometry turbocharger to regulate air intake.
  2. Compression Stroke:
    • During the compression stroke, the piston moves upward, compressing the air in the combustion chamber to high pressures and temperatures.
    • The compression ratio in diesel engines is much higher than in gasoline engines, typically ranging from 15:1 to 22:1. This high compression ratio is necessary for the air to reach temperatures sufficient to ignite the diesel fuel.
  3. Fuel Injection:
    • As the air reaches the desired compression, diesel fuel is injected into the combustion chamber at high pressure using fuel injectors.
    • The fuel injector sprays a fine mist of diesel fuel into the combustion chamber, where it mixes with the compressed air.
  4. Ignition and Combustion:
    • Unlike gasoline engines that use spark plugs for ignition, diesel engines rely on the heat generated by compressing air to ignite the fuel.
    • The high temperature and pressure conditions in the combustion chamber cause the diesel fuel to ignite spontaneously once it is injected into the chamber.
    • The ignition of diesel fuel initiates the combustion process, generating a rapid release of energy in the form of expanding gases.
  5. Expansion Stroke:
    • The rapid expansion of the combustion gases forces the piston downward, driving the crankshaft and producing power.
    • This power is used to propel the vehicle or perform other mechanical work, such as generating electricity in diesel generators or powering industrial machinery.
  6. Exhaust Stroke:
    • After the power stroke, the exhaust valve opens, and the piston moves upward to expel the combustion gases from the cylinder.
    • The exhaust gases exit the cylinder and flow through the exhaust system, where they are treated to reduce emissions before being released into the atmosphere

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

Royal Enfield Swagman silencer - King Indian - YouTube

 

Pollution  from Traditional IC Engines

  • There are various types of emissions from petrol and diesel engines such unburnt hydrocarbon, carbon monoxide, NOx and SOX
  • These emissions can results in the formation of smog in atmosphere
  • It is essential to control or minimize the unwanted emissions by adapting fuel efficient and eco-friendly combustion technologies

Methods to  Controls Emission

  • Noways, various mechanisms have been deployed with combustion chamber in order to reduce emissions such as programmer controlled fuel injector, exhaust emission reduction using selective catalytic converter and particulate traps
  • The NOx formed in IC engine is allowed to pass through selective catalytic reduction )
  • The SCR unit is placed in 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 four wheelar, the SCR unit and muffler are also placed in exhaust duct before the silencer to reduce particulate matters and emissions.
  • To provide the accurate air fuel mixture ratio, many modern combustion controlling techniques have been implemented in many cars and truck such as  MPFI, CRDI, CRDI VCR, GDI, etc. These methods ensure fuel efficient combustion.

  • Exhaust systems are significantly modified with EGR (exhaust gas re-circulation), Advanced catalytic converters,  SCR( selective catalyst reduction),  Urea after treatment devices and  particulate filters

  • Catalytic Converter for four wheelar
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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 exhaust
    • PM capture unit

Petrol Engine

  • Improved the combustion process  (by fuel injection or twin spark plug )
  • Better combustion fuel efficiency
  •  Introduction of EFI instead of carburetor
  • Better fuel quality  (higher octane number).

Diesel Engines

  • Modification in exhaust system
  •  Introduction of DPF (Diesel Particulate Filter)  in order to reduce the soot emitted from diesel engines.
  • Reduction the Sulfur content in the exhaust which makes more cleaner
  • SCR (Selective Catalytic Reduction)  in the exhaust system to reduce NOx level
CFD Simulation- Mesh Model of IC Engine

CFD Modeling for Engine Technology

Computational fluid Dynamics (CFD) plays a crucial role in the advancement and optimization of combustion technology, particularly in Internal Combustion (IC) engines. Here are some aspects that highlight the scope of CFD in the context of combustion technology for IC engines:

  1. Combustion Process Simulation:
    • CFD enables detailed simulations of the combustion process within the engine cylinder. This includes modeling fuel injection, ignition, flame propagation, and pollutant formation.
    • The ability to simulate the entire combustion cycle helps engineers understand the dynamics and interactions, leading to improved combustion efficiency and reduced emissions.
  2. Optimization of Combustion Chamber Design:
    • CFD allows for the optimization of combustion chamber geometry, including piston bowl shape, cylinder head design, and valve configurations.
    • Engineers can study different designs virtually, assessing their impact on turbulence, mixing, and heat transfer, leading to more efficient and cleaner combustion.
  3. Fuel Injection System Analysis:
    • CFD simulations help in analyzing and optimizing fuel injection systems, including the design of fuel injectors, spray patterns, and atomization.
    • Understanding how fuel is distributed and mixed with air is crucial for achieving efficient combustion and minimizing emissions.
  4. Pollutant Formation and Emission Prediction:
    • CFD models can predict the formation of pollutants such as nitrogen oxides (NOx) and particulate matter during combustion.
    • This capability aids in the development of strategies to reduce emissions and comply with environmental regulations.
  5. Transient Combustion Analysis:
    • CFD allows for transient simulations, enabling the analysis of engine behavior under different operating conditions and load changes.
    • Understanding transient combustion is essential for designing engines with responsive performance and efficient fuel consumption.
  6. Heat Transfer Analysis:
    • CFD models assist in the analysis of heat transfer within the engine components, including the cylinder walls, pistons, and cylinder head.
    • Optimizing heat transfer is crucial for preventing overheating, improving thermal efficiency, and ensuring engine durability.
  7. Combustion Stability and Knock Prediction:
    • CFD simulations can predict combustion stability and the occurrence of knock (uncontrolled combustion), providing insights into factors affecting engine performance and reliability.
  8. Alternative Fuels and Combustion Strategies:
    • CFD is valuable for evaluating the combustion characteristics of alternative fuels and exploring advanced combustion strategies, such as Homogeneous Charge Compression Ignition (HCCI) or stratified combustion.
  9. Integration with Experimental Data:
    • CFD results can be validated and refined using experimental data, creating a synergistic approach for accurate predictions and reliable simulations.
  10. Reducing Development Time and Costs:
    • CFD allows for a virtual prototyping approach, reducing the need for extensive physical testing and accelerating the development process.

Conclusion

  • The scope of CFD for combustion technology in IC engines is broad and encompasses various aspects of the combustion process, from fuel injection to emissions formation.
  • The ability to simulate and optimize these processes contributes significantly to the development of more efficient, cleaner, and reliable internal combustion engines.

2 thoughts on “Combustion Technologies in IC Engines and Its CFD Modelling”

  1. The approaches based on the development of biofuel kinetic models are largely followed to overcome the uncertainties and the complexity of the combustion occurring for this kind of fuels, as they are generally blended with gasoline in different percentages in SI engines for anti-knocking purposes. However, the chemical complexity and the uncertainties related to the measurements of these components lead researchers to rely on the idea of surrogate fuel model, that mimics the real fuel chemical and physical characteristics, employing less number of hydrocarbons components and requiring less computational time. Indeed, each fuel component should require its own set of combustion species and reactions but the resulting mechanism would be computationally prohibitive.

    Reply
    • Yes, chemical kinetics of HC rich fuel is well known and chemical mechanisms like SAGE in CONVERGE are developed for CFD modelling. By adding other species in biofuel (blended fue1) makes difficult for modelling reactions in IC engine combustion.

      Reply

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