BASIC ENGINE MEASUREMENTS

The basic measurements required to be carried out to evaluate the performance of an engine are as follows:

1. Speed
2. Fuel consumption
3. Air consumption
4. Smoke density
5. Brake power
6. Indicated power and friction power
7. Heat loss to cooling water
8. Heat going to exhaust
9. Exhaust gas analysis

1. Speed Measurement: The angular speed of engine (crankshaft) may be measured by a tachometer. Tachometers may be classified into the following categories:
   1. Mechanical tachometers
   2. Electrical tachometers
   They can further be classified as contact type and non-contact type. Contact type tachometers are of the following types:
   1. Mechanical type: Revolution counter and timer, slipping clutch tachometers, and centrifugalfree tachometers.
   2. Electrical type: Drag cup tachometer, electromagnetic tachogenerator. Non-contact type tachometers are photoelectric tachometer, variable reluctance tachometer, stroboscope, and capacitance pick up tachometer.
2. Fuel consumption measurement: The fuel consumption of an engine is measured by determining the volume flow in a given time interval and multiplying by the specific gravity of the fuel. Another method is to measure the time required for consumption of a given mass of fuel. Accurate methods for fuel measurement are as follows:
   1. Two glass-chambers method
   2. Rotameter
   3. Positive displacement meter
3. Measurement of air consumption: Accurate measurements for air consumption can be carried out by the following methods:
   1. Orifice chamber method
   2. Viscous-flow air meter
4. Measurement of exhaust smoke: A smoke meter is a sort density measuring device and may be used to measure exhaust smoke.
5. Measurement of heat carried away by exhaust gases: An exhaust gas calorimeter is commonly used for the measurement of heat carried by exhaust gases.Mass of air supplied per kg of fuel,Heat carried away by exhaust gas per kg of fuel,where (m_a + 1) = mass of exhaust gases formed per kg of fuel suppliedc_pg = specific heat of exhaust gases, kJ/kgkT_ge = temperature of exhaust gases coming out from engine, °CT_a = temperature of ambient air, °C
6. Measurement of heat carried away by cooling water: The heat carried away by cooling water is generally measured by measuring the water flow rate through the cooling jacket and the rise in temperature of water during flow through the engine. The inlet and outlet temperatures of water are measured by thermometers inserted in the pockets provided at the inlet and outlet from the engine. The quantity of water flowing is measured by collecting the water in a bucket for a specified period.Heat carried away by cooling water,where m_w = mass of water collected /minc_pw = specific heat of water, kJ/kg °CT_wi = inlet temperature of water, °CT_w0 = outlet temperature of water, °C