Pre - ignition process in S.I Engine

Pre - Ignition is defined as the phenomenon of ignition of the charge before the ignition spark occurs. This type of ignition is caused when some parts of the combustion space e.g. spark plug , exhaust valve, carbon particles in the combustion chamber are over heated under certain operating conditions. When pre-ignition occurs , it is the equivalent of an advanced spark and may cause detonation. Conversely, when detonation is severe and long continued, it may heat up the spark plug points or carbon particles.

Pre - Ignition may cause high rates of pressure rise due to multiple ignition points and advanced timing together with irregular detonation. Pre - Ignition leads to increase in pressure before the piston the reaches TDC and hence the piston movement is opposed and the power output is reduced.

In Heavy - duty engine, excessive heating due to the pre ignition may cause piston and cylinder damage. In multi cylinder engines pre - ignition may develop in one or more cylinders, then the remaining cylinder will take full load and hence probably result in piston seizure followed by the breaking up of the piston with the catastrophic results to the whole engine.

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ELECTRICAL COMPARATORS AND ITS WORKING

Electrical Comparators are used as a means of detecting and amplifying small movements of a work contacting elements. An electrical comparator consists essentially of a pick-up head or transducer for converting a displacement into a corresponding change in current and a meter or recorder connected in the circuit to indicate the electrical change, calibrated to show in terms of displacement. Generally, an amplifier is needed to provide the requisite sensitivity and to match the characteristics of different parts of the circuit. Electrical comparators can be classified according to the electrical principle used in the pick-up head. Most of the comparators use either a differential transformer, an inductance bridge, a strain gauge or a capacitor as a means of detecting movement of the gauging element. There are different types of electrical comparators. One kind called an electrolimit gauge is used to check or measure the outside diameter of a roll. The object to be checked is place

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Mechinopedia For Mechanical Engineers

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