The implementation of the IFP-developped Compressed Air Assisted Fuel Injection process (named IAPAC) on a two-stroke engine allows the introduction of the fuel separately from the scavenging air in order to minimize fuel short-circuiting. The IAPAC process does not require an external air pump since the compressed air used to atomize the fuel is supplied, at no expense, by the crankcase. The premixed charge is delivered directly into the cylinder with a high spray quality and its stratification, for optimized combustion, is controlled by a valve. This process, therefore, provides the advantages of the direct injection but uses conventional low-pressure automotive type injection technology with commercially available gasoline injectors.
In earlier work, we showed how the qualities of light weight, compactness, high specific power, high efficiency and low emissions make this concept particularly well-adapted for future automotive applications.
Marine engine exhaust emissions from most conventional 2-stroke engines are excessive, and future legislation will no doubt take this fact into account. In this paper,we show how IAPAC technology provides an interesting solution to significantly reduce the pollutant emissions and improve the fuel economy of 2-stroke outboard engines.
A 3-cylinder 1,2 L marine outboard IAPAC 2-Stroke engine has been developed and extensively tested. The results obtained point out that, with maintained quality of compactness and power output, this new engine gives fuel consumption reductions of more than 25 % and unburned hydrocarbon emission reductions of 70 to 90 %.
Pollutant emissions are evaluated according to the ICOMIA procedure and the results clearly show how the IAPAC system is well adapted to take optimum advantage of the two-stroke cycle principle in marine outboard engines applications.