At present, engineers have the most interesting areas of research, on various operating conditions of I.C. Engine. Presently, pollution due to the I.C. Engine has got more attention, so most of the topics involved are, to reduce the pollution and maximize the fuel efficiency of the engine. There are several parameters involved to search on these areas like most of the researches are going on combustion analysis, in which the study is based on exhaust gases emitted from I.C. engine and the ignition analysis in which the study is based on to run the engine at various operating conditions. But in the performance of IC engine the reduction and detection of knock is very important task as knocking in engine will lead to vibrations and high emission, knocking also leads to low fuel efficiency. Hence, for better working of engine knocking should be reduced.

An internal combustion engine (ICE) is a heat engine that converts chemical energy in a fuel into mechanical energy, usually made available on a rotating output shaft. Chemical energy of the fuel is first converted to thermal energy by means of combustion or oxidation with air inside the engine. This thermal energy raises the temperature and pressure of the gases within the engine and the high-pressure gas then expands against the mechanical mechanisms of the engine.

The knock is produced due to abnormal combustion of fuel mixture before normal combustion can occurs which also leads to rapid energy release which is much higher compared to the normal combustion. This phenomenon causes high frequency pressure oscillations inside the cylinder noise and vibrations. The vibrations are measured using vibration meter which will show the intensity of knock occurred during combustion. Also by using noise meter noise in the combustion chamber can be measured which can show the intensity of knock.

Use of alternative fuels like bio diesel, LPG can reduce knock and misfire as well as additionally they enhance efficiency of the IC engine. Shankar K.S. et al. [1] investigated the MPFI gasoline engine combustion, its performance and emission characteristics by using LPG as fuel. The work has been carried out on four cylinder MPFI SI engine which is retrofitted to run with LPG injection and its combustion, performance and emission characteristics are studied. This experimental result shows that the higher thermal efficiency and therefore improved fuel economy can be obtained from SI engines running on LPG as compared to Gasoline. Also by providing variation in spark plug voltage can reduce the knock and misfire, as reduced voltages will give steady and uniform combustions.

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In this field of IC engines detection of Knock is very crucial task. Ying Wang et al. [2] investigated detection of knock and misfire in the SI engine. Two methods are used in this experiment .One is the ionic current method in which high frequency signals are added to the ionic current signals where knocking is happened, which can be detected by picking up these signals. The other is engine block vibration method. In misfire experiment, misfire can occur because of gap in the spark plug, adding carbon deposits and cutting out high voltages. The experiment proves that using the ionic current method we can easily detect the knock and misfire of I.C. Engine. J.O.Che et al. [3] investigated the detonation by using gas density fluctuation in a cylinder of I.C. engine by using spark plug. Most of the engine control systems do not have the any detonation sensors at all but they used spark plug as pick up for gas density. The voltage drop between the spark plug electrodes depends on the local gas density. Variation of gas density will affect the current and therefore, the voltage drop on the spark plug. They found the correlation between the pressure and voltage signals in experiment where detonation induced. Therefore spark plug is used as sensor for detecting detonation. Guoming G.Zhu et al. [4] presents a stochastic ignition limit control strategy utilizing the stochastic properties of the knock intensity feedback signal and demonstrates that the control system is able to operate the engine at its borderline knock limit smoothly despite the cycle to cycle combustion variability and inherent ionization signal variations owing to that stochastic nature. Morito Assano et al. [5] presents the development of an Ion current combustion control system with the better knock control method with better accuracy even in presence of tolerances variances, the time gaps as well as other environmental condition changes. In order to increase the accuracy of knock control they focused on spark plug and ignition coil. Chae et al. [6] investigates misfire diagnostics of I.C. engine on breakdown voltage measurement. They used spark plug as ion probe for investigating the knock in I.C. Engine. The new method modulation of break down voltage used for detecting the misfire of engine. In this work, applying a heightened voltage between the electrodes of the spark-plug serving as an ion probe, they have observed a new effect correlating with the misfire occurring in an engine. This new effect can be used in systems of engine control and measurement for a diagnostic of the abnormal combustion. The signals obtained by the new method are much more stable and informative than signals of ionic current. Zdenek et al. [7] presents the Ion based High-Temperature pressure sensor in which spark plug is used as pressure sensor to the pulse detonation engine. A high speed, durable, ion probe based such engines necessitates high temperature and durable (vibration resistant) devices. This investigation builds upon these capabilities to examine the quantitative pressures. In the current design, the ion probe acts as a charged capacitor. When an ionized field nears the probe, the electrical circuit is connected. The electrode on the probe discharges through the ionized field to a grounded plate. The rate of discharge indicates the strength of the ionized field which decays according to pressure.

As per the above literature survey, it is concluded that most of the work has been carried out to investigate knock and misfire of I.C. engine by using ionization current method in which spark plug is used as ion probe and the study focused on ignition analysis, but the combustion analysis is also a very important parameter in I.C. Engines, for reducing the pollution and increasing the fuel economy. Knock can be detected by measuring vibrations, noise or by using ion current method.

Avinash M. Patil1*, Mahesh V. Mane2, Nikhil S. Mane3 3

[1] Shankar K.S. and Mohanan, MPFI gasoline engine combustion, performance and emission characteristics with LPG injection, International journal of Energy and Environment vol.2, Issue-4, 2011, pp-761-770. [2] Ying Wang and Longbau zhaou, “Investigation of detection of knock and misfire of spark ignition engine with the ionic current method”, School of power and energy engineering, Proceedings of institutions of Engineers, Vol. 217, Xi‟ an Jiotong University ,Xi‟an, PR China, 1998. [3] J.O.Che, S.M.Lee, S.I.Moon,Korea, The measurement of combustion Gas density fluctuation in a cylinder of Internal combustion engine by Spark plug for detection of detonation, Inha University #253 Yonghym-Dong, Nam Gu, Inchon 402-751,2005. [4] Guoming G. Zhu, Ibrahim Haskara and Jim Winkelman, Stochastic limit control and its Application to Knock Limit Control Using Ionization Feedback, Sae Technical Paper Series 2005. [5] Morito Assano, Atsushi Ito,Tetsuo Kuma,Mitsunobu Kajitani,Manabu Takeuchi,Yoshiyuki Fukumura,Mitsushiro Izumi Further Development of an Ion current combustion control,1988. [6] J.O.Che, S.M.Lee, S.I.Moon, “The measurement of combustion Gas density fluctuation in a cylinder of Internal combustion engine by Spark plug for detection of detonation”, SAE Korea, Inha University, 253 Yonghym-Dong,Nam Gu,Inchon 402-751,Korea. [7] Jeffrey S. Zdenek, Relph A. Anthenien, “Ion based High-Temperature Pressure Sensor, American Institute of Aeronautics and Astronautics, AIAA-2004-0470. [8] Ingemar Andersson, “cylinder pressure and Ionization current modelling for spark ignited engines”, Linkoping studies in science and technology, Thesis No.962, 2002. [9] Lars Nielsen and Lars Eriksson, An Ion-Sense Engine Fine –Tuner, 0272-1998 IEEE

Department of Mechanical Engg, PVPIT, Budhgaon