Glossary Combustion

A/F: Air/Fuel ratio.

BDC: Bottom Dead Center. When the piston is at the bottom of the cylinder, at its lowest position in the stroke.

BMEP: Brake Mean Effective Pressure. Mean and constant pressure over the piston which would give an engine torque similar to the real mean torque obtained during power stroke.

BSFC: Brake Specific Fuel Consumption. Measure of the fuel efficiency of any prime mover that burns fuel and produces rotational, or shaft, power. It is typically used for comparing the efficiency of internal combustion engines with a shaft output.

CA50: Crank angle position where 50% of the heat is released.

CA70: Crank angle position where 70% of the heat is released.

CAD: Crank Angle Degree.

CAI: Controlled Auto Ignition.

CI: Compression Ignition.

CR: Compression Ratio. Value that represents the ratio of the volume of engine combustion chamber from its largest capacity to its smallest capacity. It is a fundamental specification for many common combustion engines.

DI: Direct Injection.

EGR: Exhaust Gas Recirculation – Help controlling NOx emission.

F/A: Fuel/Air ratio. Mass ratio of fuel to air present in an internal combustion engine

FMEP: Friction Mean Effective Pressure. Theoretical mean effective pressure required to overcome engine friction, can be thought of as mean effective pressure lost due to friction.

HCCI: Homogeneous Charge Compression Ignition.

IMEP: Indicated Mean Effective Pressure. Mean effective pressure calculated from in cylinder pressure, average in cylinder pressure over engine cycle (720° in a 4 stroke, 360° in a 2 stroke).

ISFC: Indicated Specific Fuel Consumption. Specific fuel consumption based on the engine in-cylinder pressures.

Knock: Undesired auto-ignition appearing in unburned area of combustion chamber.

LHV: Lower Heating Value. Determined by subtracting the heat of vaporization of the water vapor from the higher heating value

MFB: Mass Fraction Burned. A normalized quantity with a scale of 0 to 1, describing the process of chemical energy release as a function of crank angle

MFB10: Crank Angle for 10% MFB.

MFB50: Crank Angle for 50% MFB.

MFB90: Crank Angle for 90% MFB.

Pcyl: Cylinder pressure.

PCP: Peak Cylinder Pressure.

rc: Compression ratio.

SA: Spark Advance. spark timing expressed in crank angle degrees (compared to TDC).

SI: Spark Ignition. Common denomination for spark ignited engines.

SOI: Start Of Injection. Injection timing expressed in crank angle degrees (compared to TDC).

Tcyl: Cylinder temperature.

TDC: Top Dead Center. When the piston is at the top of the cylinder, at its highest position in the stroke.

Ti: Injection duration, generally expressed in microseconds.

Vc: Clearance Volume. Volume of the combustion chamber when piston is at TDC.

Vd: Swept volume. Volume of the cylinder between TDC and BDC piston position.

Vt: Total volume. Maximum cylinder volume.

λ: Relative Air/Fuel ratio. Ratio of actual A/F ratio to stoichiometry for a given mixture. λ= 1.0 is at stoichiometry, rich mixtures λ < 1.0, and lean mixtures λ > 1.0.