DIESEL ENGINE PRINCIPLE BASIC AND TUTORIALS

The diesel engine is an engine in which the cylinder is charged with air, which is then compressed until it is hot enough to ignite fuel injected into the combustion space. The fuel is ignited by the hot air, and the expanding gases drive the piston down on the power stroke.

The compression ratios of diesel engines cover an approximate range from 12:1 to as high as 23:1. Engine types fall into two categories: twostroke cycle and four-stroke cycle.

There are many types of combustion chamber designs which manufacturers use to mix fuel and air. There are claimed advantages for each type.

These may be fuel economy, ability to make use of simpler fuel systems, wide speed-range coverage, or firing pressure minimization. These systems generally fall into an open-chamber (Fig. 6.90) or divided-chamber (Fig. 6.91) category.


The open chamber design has the advantage of easier starting and has less heat rejected to the cooling system, but has greater demands on the injection system.The divided-chamber engines can operate with less sophisticated injection equipment since the air and fuel mixing is aided by more rapid air motion.

Better fuel economy can be attained with an open-chamber design, while a divided chamber permits lower emissions. Engines are frequently turbocharged to increase the horsepower taken from a given displacement engine.

Turbocharging utilizes some of the waste heat energy and velocity of engine exhaust gas to drive a turbine connected to a high-speed centrifugal compressor.The power from a given package size can be more than doubled, provided the engine components are strong enough to withstand the higher cylinder pressures.

The highly turbocharged engines usually have a means of reducing the air temperature after the air leaves the compressor by means of an air-to-air cooler or an air-to-water cooler.These devices are known as charge air coolers, aftercoolers, or intercoolers.


Performance Characteristics
The performance of a diesel engine is affected by air temperature, air pressure, and humidity. Correction factors are employed to ensure that the power specified takes into account the losses that are expected with altitude or temperature conditions at the site.

These correction factors are usually specified by the Society of Automotive Engineers (SAE), German Industry Standards (DIN), British Standards (BS), or the International Organization for Standardization (ISO).

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