Potential of Ozone to Enable Low Load Operations of a Gasoline Compression Ignition (GCI) Engine 2017-01-0746
Gasoline Compression Ignition (GCI) engines based on Gasoline Partially Premixed Combustion (GPPC) showed potential for high efficiency and reduced emissions of NOx and Soot. However, because of the high octane number of gasoline, misfire and unstable combustion dramatically limit low load operating conditions. In previous work, seeding the intake of the engine with ozone showed potential for increasing the fuel reactivity of gasoline. The objective of this work was to evaluate the potential of ozone to overcome the low load limitations of a GCI engine. Experiments were performed in a single-cylinder light-duty CI engine fueled with 95 RON gasoline. Engine speed was set to 1500 rpm and intake pressure was set to 1 bar in order to investigate typical low load operating conditions. In the first part of the work, the effect of ozone on gasoline autoignition was investigate while the start of the fuel injection varied between 60 CAD and 24 CAD before TDC. Results showed that earlier injection timings improved the promoting effect of ozone on gasoline autoignition mainly because of the extension of the fuel-ozone residence time. Moreover, results showed how the nitrogen monoxide (NO) contained in the residual burn gases can react with O3 molecules before they can decompose releasing the O responsible for the autoignition enhancement. In the second part of the work, results showed that seeding the intake of the engine with of 383 ppm of ozone, allowed to improve the gasoline reactivity and to reduce the intake temperature from 130°C to 40°C at a constant IMEP of 3 bar. Analysis showed that while ozone is employed to reduce the intake temperature, combustion initiated and developed at lower temperature with advantages in term of NOx emissions. Also unburned hydrocarbon HC emission reduced, while CO emission increased. In order to take advantage of the effect of ozone, the injection strategy had to be adapted: a first injection during the intake stroke was necessary to get the promoting effect of ozone while a second injection during compression stroke was employed to induce the fuel stratification necessary for controlling the combustion phasing and to avoid excessive heat release rate.