05-01-2013, 02:47 PM
IC ENGINE TESTING
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INTRODUCTION
At a design and development stage an engineer would design an engine with certain aims
in his mind. The aims may include the variables like indicated power, brake power,
brake specific fuel consumption, exhaust emissions, cooling of engine, maintenance free
operation etc. The other task of the development engineer is to reduce the cost and
improve power output and reliability of an engine. In trying to achieve these goals he has
to try various design concepts. After the design the parts of the engine are manufactured
for the dimensions and surface finish and may be with certain tolerances. In order verify
the designed and developed engine one has to go for testing and performance evaluation
of the engines.
Thus, in general, a development engineer will have to conduct a wide variety of engine
tests starting from simple fuel and air-flow measurements to taking of complicated
injector needle lift diagrams, swirl patterns and photographs of the burning process in
the combustion chamber. The nature and the type of the tests to be conducted depend
upon various factors, some of which are: the degree of development of the particular
design, the accuracy required, the funds available, the nature of the manufacturing
company, and its design strategy. In this chapter, only certain basic tests and
measurements will be considered.
Objectives
After studying this unit, you should be able to
• understand the performance parameters in evaluation of IC engine
performance,
• calculate the speed of IC engine, fuel consumption, air consumption, etc.,
• evaluate the exhaust smoke and exhaust emission, and
• differentiate between the performance of SI engine and CI engines.
80
Applied Thermal
Engineering
PERFORMANCE PARAMETERS
Engine performance is an indication of the degree of success of the engine performs its
assigned task, i.e. the conversion of the chemical energy contained in the fuel into the
useful mechanical work. The performance of an engine is evaluated on the basis of the
f
ollowing :
(a) Specific Fuel Consumption.
(b) Brake Mean Effective Pressure.
© Specific Power Output.
(d) Specific Weight.
(e) Exhaust Smoke and Other Emissions.
The particular application of the engine decides the relative importance of these
performance parameters.
For Example : For an aircraft engine specific weight is more important whereas for an
industrial engine specific fuel consumption is more important.
For the evaluation of an engine performance few more parameters are chosen and the
effect of various operating conditions, design concepts and modifications on these
parameters are studied. The basic performance parameters are the following :
(a) Power and Mechanical Efficiency.
(b) Mean Effective Pressure and Torque.
© Specific Output.
(d) Volumetric Efficiency.
(e) Fuel-air Ratio.
(f) Specific Fuel Consumption.
(g) Thermal Efficiency and Heat Balance.
(h) Exhaust Smoke and Other Emissions.
(i) Specific Weight.