PERFORMANCE PARAMETERS

The performance of an engine is an indication of the degree of success with which the conversion of chemical energy contained in the fuel is done into useful mechanical work. The degree of success is compared on the basis of following parameters:

1. Specific fuel consumption (SFC)
2. Brake mean effective pressure (BMEP)
3. Specific power output (SP)
4. Specific weight (SW)
5. Exhaust smoke and other emissions

However, in the evaluation of engine performance, the following performance parameters are chosen:

1. Power and mechanical efficiency
2. Mean effective pressure and torque
3. Specific output
4. Fuel-air ratio
5. Volumetric efficiency
6. Specific fuel consumption
7. Thermal efficiency and heat balance
8. Exhaust smoke and other emissions
9. Specific weight

Indicated power,

where p_im = indicated mean effective pressure, Pa

L = Length of stroke, m

A = Area of stroke, m²

N = rotational speed, rpm

n = number of strokes per revolution

= 2 for four-stroke engine

= 1 for two-stroke engine

where p_bm = brake mean effective pressure, Pa

Specific output: It is defined as the brake output per unit of piston displacement.

Volumetric efficiency,

= v_a /v_s

Brake specific fuel consumption,

where m_f = mass of fuel consumed, kg

t = time in minutes

Indicated specific fuel consumption,

where LCV = lower calorific value of fuel, kJ/kg

where η_a = air standard efficiency

Exhaust smoke and other emissions: Oxides in nitrogen, unburned hydrocarbons, etc.