Stages of SI Engine Combustion

The period between the spark and the start of the combustion

Higher self-ignition temperature fuels result in longer ignition lag.

Mixture richer than stoichiometric results in a shorter ignition lag.

Increased load increases cycle pressures and flame speeds.

Increased turbulence increases flame speed.

Increased engine speed increases mixture turbulence and thus flame speed.

Engines of similar design generally run at the same piston speed, achieved through varied RPM based on engine sizes.

The delay between the spark and the start of the combustion process.

Higher intake temperature and pressure, increased compression ratio, and faster chemical reaction rate help reduce the time it takes for the mixture to burn.

Engine supercharging, optimal spark timing, and residual gases within the engine at the end of the exhaust stroke increase combustion speed.

Premature ignition of the fuel-air mixture before the spark plug ignites it, causing a loud noise and potential engine damage.

Spontaneous ignition of the fuel-air mixture without the spark, leading to combustion.

The ignition of the fuel-air mixture due to contact with hot surfaces before the spark plug ignites it.

The proportion of air to fuel in the air-fuel mixture, affecting combustion rate and heat generation.

The ratio of the maximum volume to the minimum volume in the combustion chamber, impacting the pressure and temperature during combustion.

The speed at which the flame spreads within the combustion chamber.

The distance between the spark plug electrodes, affecting the voltage required to create a spark.

The chaotic mixing of air within the combustion chamber, directly related to engine speed.

A phenomenon in engines where high-pressure waves generated during combustion cause undesirable damage and reduced performance.

Exhaust valve placement should be close to the spark plug to prevent end-gas detonation.

Larger engines are more prone to knocking because the flame has a longer distance to travel through the combustion chamber.

Decreasing turbulence in the fuel-air mixture lessens flame speed, increasing the chance of knocking.

Fuel molecular structure (like paraffin) and the fuel-air ratio affect the engine's tendency to knock.

Higher compression ratios increase engine temperature and pressure, elevating the risk of knocking.

A dangerous combustion type resulting in increased wear on parts within the engine.

Knocking leads to the formation of more carbon deposits on engine components.

Engine knocking increases heat transfer to the combustion chamber walls.

Knocking reduces engine power production and overall efficiency due to wasted energy and higher heat transfer.

Causes additional heat transfer to the engine walls.

Uncontrolled combustion in a diesel engine, characterized by a sharp, audible noise.

Different stages of fuel burning in an engine: rapid pre-mixed, controlled diffusion, and afterburning.

The time between fuel injection and the start of combustion in a diesel engine.

A measure of a diesel fuel's ignition quality.

The point in the engine cycle when fuel is injected into the cylinder.

The amount of fuel injected into the cylinder.

Temperature and pressure of air entering the engine.

RPM of the engine.

Shape and structure of the engine's combustion area.

Increased temperature and density of air from supercharging lead to a higher tendency for engine knocking.

Lower coolant temperature delays combustion, leading to increased knock tendency. Higher temperatures, vice-versa.

Different combustion chamber designs affect the temperature of the end gases and thus their ignition vulnerability to knocking.

Spark timing affects the amount of fuel burnt in an engine cycle, before and after top dead centre (TDC).

Longer flame travel distances increase the risk of knocking.

A centrally located sparkplug in a combustion chamber can reduce the possibility of knocking.

The time between the fuel injection and the start of combustion.

The process of breaking fuel into small droplets for better mixing.

The rate of swirl affects evaporation and air-fuel mixing, which in turn impacts combustion, but is typically less notable.

Low oxygen in a combustion chamber increases ignition delay, thus potentially increases knocking.