The test consists of making, in turn, each cylinder of the engine inoperative and noting the reduction in brake power developed. This method can be used only for multi – cylinder IC engines This method requires elaborate equipment to obtain accurate indicator diagrams at high speeds. The indicated power is obtained from an indicator diagram and brake power is obtained by a brake dynamometer. Power is obtained by computing the difference between the indicated power and brake power. The directional margin of error is rather wide because the graph is not exactly linear.įrom the Measurement of Indicated Power and Brake Power:- This is an ideal method by which friction The main draw back of this method is the long distance to be extrapolated from data between 5 and 40 % load towards the zero line of the fuel input. This method of measuring friction power will hold good only for a particular speed and is applicable mainly for compression ignition engines. This energy in the fuel would have been spent in overcoming the friction.
brake power = 0, it consumes a certain amount of fuel. Further when the engine does not develop power, i.e. Hence the extrapolated negative intercept of the horizontal axis will be the work representing the combined losses due to friction, pumping and as a whole is termed as the frictional loss of the engine. As shown in the figure, in most of the power range the relation between the fuel consumption and brake power is linear when speed of the engine is held constant and this permits extrapolation. The intercept of the negative axis is taken as the friction power of the engine at that speed. In this method a graph of fuel consumption (vertical axis) versus brake power (horizontal axis) is drawn and it is extrapolated on the negative axis of brake power (see Fig). This method is also known as fuel rate extrapolation method. The friction loss is made up of the energy loss due to friction between the piston and cylinder walls, piston rings and cylinder walls, and between the crank shaft and camshaft and their bearings, as well as by the loss incurred by driving the essential accessories, such as water pump, ignition unit etc.įollowing methods are used in the laboratory to measure friction During suction and exhaust strokes the piston must move against a gaseous pressure and power required to do this is called the “pumping losses”. Electric Dynamometer I.Eddy current Type Dynamometer II.Swinging Field Dynamometerįriction Power Friction power includes the frictional losses and the pumping losses. Hydraulic Dynamometer B.P=WN/K Watts W =Weight measured on the dynamometer, N K=Dynamometer constant (60*1000/2*pi*R) and N=RPM of the engine.ģ. T = Torque = (W-S) De/2 W = Load on the Brake Drum in N S = Spring Balance Reading in N De = Effective Brake Drum Diameter = Drum Diameter(Db) + (2*Thickness of Rope) BP can also be written asīP = (W-S) (Db +d).N Π (Db+d) is circumference of the brake drumĢ. Pm= Pmep = (s*a)/l = N/m2 Where: a = actual Indicator diagram cm2 l = base width of the indicator diagram, cm s = spring value or spring constant used for in indicator diagram,( N/m 2 )/cmīrake mean effective pressure (BMEP) - Mean effective pressure calculated from brake torqueġ. Mean Effective Pressure is also obtained by engine indicator diagram as W = work per cycle in joule P = power output in watt pmep = mean effective pressure in pascal Vd = displacement volume in cubic metre nc = number of revolutions per cycle (for a 4-stroke engine nc = 2) N = number of revolutions per second T = torque in newton-metre Pi = (Net work of cycle)/Swept Volume in N/m2 Mean Effective Pressure The mean effective pressure is a quantity related to the operation of an reciprocating engine and is a valuable measure of an engine's capacity to do work that is independent of engine displacement Indicated Mean Effective Pressure or imep (pi) - it may be defined as the average pressure over a cycle in the combustion chamber of the engine.
L is the stroke length, in m A is the area of cross section of the piston, m 2, N’ is the engine speed in rev/min, n is the number of cylinders andįor 4-stroke engine-one cycle will be completed in two revolutions N’=N/2 For 2-stroke engine-one cycle will be completed in one revolutions N’=N
Pi is the indicated mean effective pressure, in N/m Indicated Power Power obtained at the cylinder. POWER AVAILABLE AT THE END OF CRANK SHAFT: BP INDICATE POWER DEVELOPED INSIDE THE ENGINE: IP (i) Specific Weight.Įngine Testing and Performance Indicated Power (IP) = Brake Power (BP) - Friction Power (FP) engines are as follows: (a) Power and Mechanical Efficiency. Engine Testing and Performance Important Performance Parameters of I.C.Engines:The important performance parameters of I.C.