Is a High Pressure Direct Injection System a Solution to Reduce Exhaust Gas Emissions in a Small Two-Stroke Engine?

摘要

Small gasoline engines are used in motorcycles and handheld machinery, because of their high power density, low cost and compact design. The reduction of hydrocarbon emissions and fuel consumption is an important factor regarding the upcoming emission standards and operational expenses. The scavenging process of the two-stroke engine causes scavenging losses. A reduction in hydrocarbon emissions due to scavenging losses can be achieved through inner mixture formation using direct injection (DI). The time frame for fuel vaporization is limited using two-stroke SI engines by the high number of revolutions. A high pressure DI system was used to offer fast and accurate injections. An injection pressure of up to 140 MPa was provided by a common rail system, built out of components normally used in automotive engineering. A standard electromagnetic injector is applied for the fuel injection. This injection unit is dimensioned for multi-point injections in diesel engines. It allows short injection durations and thus low injection rates. An air-assisted direct injection system was investigated to show the potential of a low-cost solution for direct injection. A controlling unit linked to the test rig software provides the signals for the injector. The fuel pressure in combination with the injector controlling unit allows flexible adjustment of injection parameters during the investigations. Another topic of these investigations is the use of alternative fuels. These fuels show high potential for further reduction of exhaust emissions while simultaneously increasing the engine power output.