Highly Homogeneous Compression Ignition in a Direct Injection Diesel Engine Fuelled with Diesel and Biodiesel 2007-01-2020
Highly homogeneous compression ignition is difficult to achieve in a direct injection diesel engine. The difficulty of achieving adequate fuel vaporization and the problems of fuel spray wall impingement are the main factors. Limitation of the maximum operating load results from high rates of pressure rise that occur in this combustion regime. The levels of HC and CO emissions are raised substantially when compared with conventional combustion and remain a significant emission factor.
In this study, two methods of achieving highly homogeneous combustion in a direct injection diesel engine were investigated, Nissan MK type and early injection. The effects of fuel injection pressure, injection timing, EGR level, EGR cooler efficiency and compression ratio were examined using a conventional 4 cylinder 2.0L common rail diesel engine with 18.4:1 and 14.4:1 compression ratios.
In view of the current interest in biofuels, diesel and biodiesel fuel were used to examine the effect of fuel oxygenation in combination with highly homogeneous combustion methods on the emissions of HC, CO, smoke and NOx. This was done by the measurement of gaseous exhaust emissions, filter smoke emissions and in-cylinder pressure from which heat release rates and in-cylinder pressure rise rates were calculated.
An increase in the highly homogeneous charge operating range was possible when the reduced compression ratio was used. At low load, NOx and smoke emissions remained negligible with diesel and biodiesel and a reduction in HC and CO was seen with biodiesel fuel. At higher load, smoke emissions became more significant and a reduction of this emission was seen with biodiesel. A summary of direct injection diesel methods for low emissions is presented and the suitability of oxygenated biodiesel with these regimes is analyzed.