Today we will discuss about main parameters used to test a engine performance. Engine testing is very important part of engine design. The engine
performance indicates by the term efficiency. For the testing basis, five major efficiencies
are used which we have discussed in the last post. If you have not read the last
article first read it from here.
Engine testing parameter to design an engine:
To test and designate an engine, five major efficiencies and
five other parameters are used. These are:-
6. Mean effective pressure
7. Mean piston speed
8. Specific power output
9. Specific fuel consumption
10. Air fuel Ratio
These parameters are described
below:
1. Mean Effective Pressure:
It is the average pressure
inside the cylinder of an internal combustion engine. It is based on the
measured power output. For any particular engine there is a specific mean
effective pressure. The mean effective pressure is describe by the ratio of the
power output of the engine to the volume of the it. When we used indicate
power to calculate mean effective pressure known as indicate mean effective pressure and when we used brake power the
pressure is known as the brake mean effective pressure. The maximum brake mean
effective pressure for turbocharged and supercharged engine is higher than
natural aspired engine.
2. Mean piston speed:
It is one of the main parameter
of an engine. It is describe in the meter per second. it is the more important
than the crank rotation speed because it does not depend on size of piston and
cylinder. It is define as
Sp = 2LN
Where L is length of the
cylinder and N is the crank rotation speed. The range of mean piston speed is 8
to 15 m/s.As the engine size
increases the mean piston speed decreases.
3. Specific power output:
It is define as power
output per unit piston area. It is measure of the engine designer success in
using the available piston area. It is proportional to the product of mean
effective pressure and mean piston speed.
So it is clear that power of an engine increase by increase either of
mean effective pressure or specific piston speed or both.
Brake power output / Piston Area
4. Specific fuel consumption:
It is the amount of fuel consumption
in kilogram to produce per kilowatt hour energy. It is reflects the engine performance
of efficient of engine. It is also describe
the fuel consumption per unit time to power. According to power used it has
also two types brake specific fuel consumption and indicates specific fuel
consumption.
Fuel consumption per unit time / Power
5. Air fuel ratio:
It is the ratio of mass of
air to mass of fuel used per power stroke. Air fuel ratio of CI engine is high
compare to SI engine. The air fuel ratio
of SI engine is about 15:1 and for CI engine is about 18:1 for full load to
80:1 for no load.
mass of air per cycle / mass of fuel per cycle
These are the main engine parameters are used to test a engine performance. If you have any query ask by commenting.