Mechatronics for water injection in SI engine

Abstract

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. 1m3) 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.