CI Engine:(kind of engine)
Old:
The compression ignition (CI) engine operates with a heterogeneous charge of previously compressed air and finely divided spray of liquid fuel. The latter is injected into the engine cylinder towards the end of the compressor when, after a suitably intensive mixing process with the air already in the cylinder, the self ignition properties of the fuel cause combustion to be initiated frm small nuclei . These spread rapidly so that complete combustion of all injected fuel, usually with the air- fuel ratios well in excess of stoichiometric, is ensured. The mixing process is crucial to the operation of the Diesel engine and as such has received a great deal of the attention which is reflected in a wide variety of combustion systems which may conveniently be grouped in two broad categories, viz.
a) Direct Injection (DI) Systems as used in DI engines
b) Indirect Injection (IDI) Systems as used in IDI engines
(Diesel engine reference book, Second edition, p. 5- Edited by Bernard Challen and Rodice Baranescu)
New:(beter)
In a CI engine, air and fuel remain separated until the threshold of combustion. Fuel is injected late in compression stroke, when cylinder pressure is already high.In other words, the work of compression precedes fuel injection. Injection pressures range from about 1600psi to more than 25000psi for modern designs. The amount of fuel supplied varies with load and speed requirements.
Air enters through the intakemanifold, in a manner roughly analogous to SI practice. But the air supply is unthrottled, so that the CI engine draws the same volume of air per revolution, regardless of its speed.
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