Water injection is a means of internal cooling of the engine. During combustion, excess temperatures generated are absorbed by water as latent heat. Optimum water injection quantities were found to be about 0.015 ml to 0.031 ml of water per cycle on a 592 cc SI engine. The experiments were carried out by tapping the fuel injector signal and designing a circuit to inject water at the instant petrol is injected. Fuel injection duration was tuned by using a Wide Band Lambda sensor. The engine was supercharged as well by means of compressed air supply and regulated by hysteresis control. Water injection was investigated while varying spark advance to find the Maximum Brake Torque (MBT). Maximum obtained torque improvement with water injection was 16 %. This was achieved at a manifold absolute pressure of 120 kPa, with air temperature at ambient. The same load condition, 120 kPa, with air heated to the temperature that would be obtained from isentropic compression, resulted in a torque improvement of 7 %.

Internal combustion engines are generally speaking mechanical devices but have benefitted tremendously from electronic controls. The electronic implementation of fuel injection and spark ignition on an older single-cylinder JAP engine through the use of a programmable Engine Control Unit (ECU) is discussed in this work. Furthermore the additional electronics required for water injection and boost control that were not supported by the programmable ECU are detailed. The injection of water into the Spark Ignition (SI) engine was the main objective of this study but the solution for this task through the use of electronics and LabView provided a robust and flexible system whereby the whole range of parameters could be explored. The engine was electronically controlled by the ECU through the sensing of 36 teeth that were machined in the dynamometer coupling and by having the cam sensor triggered by the maximum lift of the tappet of one of the valves. Water injection electronic circuitry was designed and built from scratch. The variable duration water injection pulse was generated by a 555 timer IC in Monostable (configuration) mode that was triggered every two engine revolutions by the fuel pulse. The duration of water injection per cycle in milliseconds was recorded by the ECU through the use of a dual potentiometer that controlled both the RC value for the 555 timer and also generated a voltage that varied linearly with water pulse duration for data logging by the ECU. Boost control of the engine from the laboratory compressed air supply was first tried to be solved by mechanical means namely manual control, an external wastegate (used as a proportional valve) and also different sized pressure regulators, however these attempts were unsuccessful. A very straightforward but ultimately functional solution was the use of an ON/OFF solenoid valve that opened compressed air (6 bar nominal) to a large (approx. 1m 3 ) tank that fed the SI engine. The ON/OFF control was performed through LabView and a specifically built solenoid driver circuit. The control of air temperature into the SI engine was also electronically controlled through ON/OFF control from LabView which controlled the water temperature of a charge-air heat exchanger. These systems were integrated together and performed as desired to test all desired water injection durations, boost levels, air inlet temperatures, spark timing and fuel quantity.

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