ENGINE PERFORMANCE AND EFFICIENCY

Your prime concern as an Engineman is to keep the machinery for which you are responsible operating in the most efficient manner possible. From your past experience and training, you know that engine efficiency and performance depend upon much more than just operating the throttle and changing oil at prescribed intervals. The preceding chapters have covered many of the casualties which may occur to reduce the power output of an engine. You have learned how to pre-vent the occurrence of many of these casualties. As you gain experience and understanding, you will probably have to train other people. The people you will train will frequently come up with many questions about why an engine does or does not perform efficiently. Will you be able to answer their questions?

To understand the various factors that influence engine performance and efficiency, a thorough knowledge of the internal combustion process is necessary. Once the combustion process is understood, it will be much easier for you to appreciate the part played by such factors as engine design, engine operating conditions, fuel characteristics, fuel injection, ignition, pressures and temperatures, and compression ratios. This chapter provides some of the information necessary for a better understanding of the many factors that affect engine performance and efficiency. As an Engineman, you will be able to gain complete understanding of such factors only through continued study and practical experience.

You should know how the power which an engine can develop is limited by such factors as the mean effective pressure, the length of piston stroke, the cylinder bore, and the engine speed. You must also know how these factors are used in determining the power developed by an engine. You must learn how heat losses, efficiency of combustion, volumetric efficiency, and the proper mixing of fuel and air limit the power which a given engine cylinder can develop. You must become familiar with the factors which cause overloading of an engine and unbalance between engine cylinders. You should know the symptoms, causes, and effects of cylinder load unbalance and the steps that are necessary to maintain an equal load on each cylinder.

You must know what is meant by engine efficiency and know how the various types of efficiencies and losses are used in analyzing the internal combustion process. You must also be familiar with those factors which may cause the efficiencies to increase or decrease, and with the ways these variations affect engine performance. Parts of this chapter may serve as a brief review, but most of the information provided deals with those factors that influence engine performance and efficiency.