Electronic Direct Fuel Injection (EDFI) for Small Two-Stroke Engines

The benefits of direct cylinder fuel injection to the fuel economy and exhaust emissions of small spark ignited two-stroke engines is well known. The selection of a commercially viable fuel injection solution continues to receive evaluation and scrutiny by the engine manufacturers.

This paper describes the development and demonstration of an EDFI solution which is applicable to low cost and high production volume engines in several industries. The system is based on the “accumulator” fuel injection operating principle, which involves pressurizing fuel within an injection nozzle and subsequently releasing the pressurized fuel into the combustion chamber on command. This concept provides very short injection duration throughout the dynamic operating range of the engine as well as high injection frequency capability. The addition of full authority electronic control to the direct fuel injection system provides control flexibility and the opportunity for speed and load dependent calibration of the fuel injection event. The combination of unique components, control schemes and combustion systems has resulted in a flexible EDFI solution which is applicable to low cost two-stroke engines. Components include a single plunger pressurizing pump, an accumulator fuel injector and a precise, magnetically latching 2-way solenoid valve. The control scheme involves both fuel quantity and timing control by means of solenoid valve timing strategy. Skip-injection strategy for improved part load or idle combustion efficiency is optional. Combustion systems which have been evaluated include hollow cone spray, conventional and piston bowl combustion chambers and spray impingement techniques.

This paper describes the EDFI hardware design and operation, the application of system simulation software for design iteration, specific application designs and test results. The design applications include a 46cc handheld utility engine and a 50cc 2-wheeler engine. The 46cc utility engine results include comparisons of power, fuel consumption and exhaust emissions. Emissions results include:

1. 1
   Data at maximum power and idle
2. 2
   Comparison to the California Air Resources Board (CARB) for the year 2000
3. 3
   Environmental Protection Agency (EPA) marine engine regulations for 2006

The 50cc 2-wheeler data includes comparisons of power and fuel consumption to a standard (carbureted) engine. Data is compared at Wide Open Throttle (WOT) and part load conditions. In addition to achieving desired fuel consumption and hydrocarbon emission reductions, test results included power increase, particularly in the range from peak torque speed to rated power speed. It is concluded that the two-stroke spark ignited engine has the potential to continue a dominant role in low cost, high power density applications while meeting regulated exhaust emission standards.