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The ionization current across the spark plug gap is obtained by applying a constant voltage using DC power source across the spark gap after the high-voltage discharge. The methodology involves study and comparison of different knock detection methods (cylinder gas pressure, accelerometer and ion current) through literature survey, development of analytical models (ionization current, chemical equilibrium, kinetic Nitric Oxides) to estimate crank angle resolved cylinder gas pressure from the measured values of ionization current. Model refinements and validations, development of Ignition Coil integrated DC power source and ion current measurement circuit, Transistorized Coil Ignition and microcontroller based knock controller have been carried out. Experiments have been conducted to validate the model with the reference method (cylinder gas pressure).

In the case of small SI engines for two-wheelers emission reduction will preferably be achieved through the use of lean mixtures since catalytic converters will increase the cost. In such cases a very close control over the air fuel ratio will be needed. In this work a carbureted 125cc small capacity two-wheeler engine was modified to operate with Port Fuel Injection (PFI) for improved control over the air fuel ratio. A throttle body was specially made to house the injector and a position sensor. A cam position sensor, crank angle sensor, manifold air pressure (MAP) sensor, 60-2 toothed wheel for precise control of the events on the angle basis were used. Extensive tests were conducted with the throttle body and fuel injector to obtain the mathematical models for the inlet manifold and fuel injector. These were used to make the model based controller. The dSPACE - Micro Auto Box platform was used to develop and test the control algorithms. Software was written using SIMULINK.

A personal computer (PC) based electronic governor was developed in this work for a diesel engine. A stepper motor was used to actuate the rack of the inline fuel pump of the engine with a bell crank lever. The digital output of the system was used to control the stepper motor using special hardware. This governor was tested under different steady and transient operating conditions. The electronic governor performed satisfactorily. In most cases the speed settled down in time duration comparable to that with the mechanical governor. The electronic governor could operate with no change in the mean speed with engine output. The performance was very sensitive to the P, I and D parameters of the control software. It was felt that the system could be improved with a stepper motor of finer steps and higher torque.

An electronic system was developed for the control of the injection timing and injected fuel quantity for studies on a passenger car engine. This system can be used to produce maps of these parameters for implementation in an electronic control unit. The complete electronic hardware which included the cam position sensor, pulse shaping, pulse delay and sequencing features was developed and tested. The system could control the injection pulse width for the different cylinders independent of each other. The developed system was used to conduct parametric studies. The results obtained were compared with that obtained from the base carbureted engine. There was a significant improvement in brake thermal efficiency and reduction in HC and CO emissions with the injection system. A retarded injection timing was needed at low loads. The volumetric efficiency of the injection system was much higher than the carbureted version.

Conventional two-stroke spark-ignition (SI) engines have difficulty meeting the ignition requirements of lean fuel-air mixtures and high compression ratios, due to their breaker-operated, magneto-coil ignition systems. In the present work, a breakerless, high-energy electronic ignition system was developed and tested with and without a platinum-tipped-electrode spark plug. The high-energy ignition system showed an improved lean-burn capability at high compression ratios relative to the conventional ignition system. At a high compression ratio of 9:1 with lean fuel-air mixtures, the maximum percentage improvement in the brake thermal efficiency was about 16.5% at 2.7 kW and 3000 rpm. Cylinder peak pressures were higher, ignition delay was lower, and combustion duration was shorter at both normal and high compression ratios. Combustion stability as measured by the coefficient of variation in peak cylinder pressure was also considerably improved with the high-energy ignition system.