Effects of variations in fuel properties on a homogeneous charge compression ignited light-duty diesel engine operated with gasoline-isobutanol blends

Abstract

Homogeneous charge compression ignition (HCCI) is a promising alternative combustion mode to conventional diesel combustion to achieve better engine performance and lower particulate matter and oxides of nitrogen emissions. In the present study, the experiments were performed in a modified light-duty diesel engine operated in port fuel injected HCCI mode with gasoline-isobutanol blends. All the experiments were performed at a constant engine speed of 1500 rpm and varying engine loads. The effects of variations in fuel properties on the achievable load range, engine performance improvement, and emission reduction were examined. The use of isobutanol, a gasoline-like high volatile, low reactivity, renewable fuel, help reduce fossil fuel dependency. A cetane improver, 2-ethyl hexyl nitrate (2-EHN), was added in a fixed proportion of 6 vol.% to all the fuel blends to attain stable HCCI combustion at lower engine loads. The volumetric proportion of isobutanol in the fuel blends was increased from 20% to 60%, while the gasoline proportion was correspondingly reduced. An algorithm to evaluate the ‘engine performance and emission indicator value’ was used to identify suitable fuel blend composition based on user-defined weights. Test results showed that the maximum achievable engine load was extended from 38% (of rated engine load) for diesel–fuelled HCCI to 70% (of rated engine load) for isobutanol-gasoline-2-EHN-fuelled HCCI. The indicated thermal efficiency improved with increased isobutanol in the fuel blends for a particular engine load. At 50% engine load, the indicated thermal efficiency improved by 40% for 60% isobutanol/ 34% gasoline/ 6% 2-EHN than 20% isobutanol/ 74% gasoline/6% 2-EHN. The HCCI combustion of isobutanol fuel blends produced very low oxides of nitrogen and soot emissions than conventional diesel combustion, and the indicated thermal efficiency was close to that of conventional diesel combustion at lower engine loads and improved at higher engine loads. At 70% engine load, the oxides of nitrogen and soot emissions were reduced by 69% and 96%, respectively, for HCCI combustion of 60% isobutanol/34% gasoline/6% 2-EHN than conventional diesel combustion. It was found that with an increase in engine load, the optimal fuel blend composition consisted of an increased concentration of isobutanol. Overall, the present study demonstrates that isobutanol is suitable for improving HCCI engine metrics.