Basic Engine operation

Basic Engine operation

1. engine geometry

2. engine power and torque

   • torque is the abilty of an engine to do work
   • power is the rate at which the engine does work.
     • indicated power is the amount of power produced in the cylinder
     • brake power is the power generated in the output shaft, this will be lower than the indicated power due to mechanical friction and parasitic loads

3. WOT = wide open throttle

   • indicated work per cycle is the integral of the Pressure vs. volume curve for given cylinder pressure volume data
     • Gross indicated work per cycle is the combination of areas wa and wc or the work generated in the expansion and compression
     • pump work: the work exerted on the gas by the piston in the intake and exhaust strokes. =Wb + Wc
     • net indicated growth- the work delivered over all 4 strokes: =wa+wc-(wb+wc) = wa -wb
   • the net indicated power of the engine decreases when at part throttle because the pressure around the throttle decreases the more it closes
     • indicated power with a supercharger: the net indicated power will increase with a supercharger as they can have positive pump work. (brings wb above the atmospheric pressure line. supercharger is parasitic load however
       • turbocharger not parasitic but backpressure raises bottom line and reduces area b

4. Mechanical efficientcy

   • MEP = mean effiective pressure = the fictual const. pressure that would give same work per cycle as engine. not effected by torque so a better engine comparison
   • frction work is the work done to overcome the friction in the engine, and will lower the net indicated work per cycle