Partially Premixed Combustion at High Load using Gasoline and Ethanol, a Comparison with Diesel

This paper is the follow up of a previous work and its target is to demonstrate that the best fuel for a Compression Ignition engine has to be with high Octane Number.

An advanced injection strategy was designed in order to run Gasoline in a CI engine. At high load it consisted in injecting 54 % of the fuel very early in the pilot and the remaining around TDC; the second injection is used as ignition trigger and an appropriate amount of cool EGR has to be used in order to avoid pre-ignition of the pilot. Substantially lower NOx, soot and specific fuel consumption were achieved at 16.56 bar gross IMEP as compared to Diesel. The pressure rise rate did not constitute any problem thanks to the stratification created by the main injection and a partial overlap between start of the combustion and main injection. Ethanol gave excellent results too; with this fuel the maximum load was limited at 14.80 bar gross IMEP because of hardware issues.

Applying the commonly used PPC injection strategies to Gasoline resulted in higher pressure oscillations after combustion and the heat transfer was enhanced. It was shown that this problem can be somehow solved by employing a late pilot injection, unfortunately the combustion is diffusion controlled and there is an increase in fuel consumption as compared to the strategy previously described.

The viability of having low fuel consumption, NOx, soot and pressure rise rate using high ON fuels in a CI engine was demonstrated using a Scania single cylinder truck engine with 2 liters displacement volume running at 1100 rpm.