A stratified charge engine is a type of internal combustion engine designed to improve fuel efficiency and reduce emissions by creating a non-uniform (stratified) air-fuel mixture in the combustion chamber. Unlike traditional homogeneous charge engines, where the air-fuel mixture is uniformly distributed, a stratified charge engine has a richer mixture near the spark plug and a leaner mixture elsewhere.
How stratified charge engine Works:
Lean Combustion Principle – The engine operates with an overall lean air-fuel ratio (higher air-to-fuel ratio than stoichiometric), improving fuel economy.
Charge Stratification – During the compression stroke, fuel is injected in a way that creates:
A rich mixture near the spark plug (ensuring reliable ignition).
A lean or air-only mixture farther away (reducing fuel consumption).
Controlled Ignition – The spark plug ignites only the rich mixture, and the flame front propagates through the lean regions.
stratified charge engine Advantages:
Better Fuel Efficiency – Lean combustion reduces fuel consumption.
Lower Emissions – Lean operation reduces nitrogen oxides (NOx) and carbon dioxide (CO₂).
Reduced Throttling Losses – Some stratified engines (like gasoline direct injection) minimize pumping losses by controlling power output via fuel injection rather than throttle position.
Disadvantages:
Complex Fuel Injection System – Requires precise high-pressure direct injection.
Higher Particulate Emissions – Lean combustion can produce more soot (a concern in gasoline engines).
Limited Load Range – Stratification is typically effective only at low-to-medium loads; engines revert to homogeneous charge at higher loads.
Applications:
Gasoline Direct Injection (GDI) Engines – Many modern GDI engines use stratified charge at low loads.
Honda's CVCC (Compound Vortex Controlled Combustion) – An early stratified charge design from the 1970s.
Diesel Engines (in a way) – Diesel engines inherently use charge stratification but rely on compression ignition rather than spark ignition.
Comparison with Homogeneous Charge Engines:
| Feature | Stratified Charge Engine | Homogeneous Charge Engine |
|---|---|---|
| Air-Fuel Mixture | Non-uniform (rich near spark, lean elsewhere) | Uniform |
| Fuel Efficiency | Higher (lean burn) | Lower |
| Emissions | Lower CO₂, but higher particulates | Higher NOx, but lower particulates |
| Complexity | More complex injection system | Simpler fuel delivery |
Conclusion:
Stratified charge engines offer a way to improve efficiency and reduce emissions, particularly in gasoline direct injection (GDI) engines. However, challenges like particulate emissions and system complexity limit their widespread adoption. Advances in injection technology and after-treatment systems (like particulate filters) continue to make stratified charge a viable strategy for cleaner, more efficient engines
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