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A brief study has been undertaken with exhaust gas recirculation (EGR) applied to a prototype low emission, heavy duty, direct injection (DI) diesel engine aimed at evaluating the potential for low nitrogen oxide (NOx) emissions. By virtue of the very low smoke levels achieved with the prototype engine, EGR can be applied at full load for substantial reductions in NOx down to c. 2.5 g/kWh (1.9 g/hph) over the European R-49 13-Mode test. These results were achieved with competitive particulates and fuel consumption and without recourse to engine de-rating. Compliance with the NOx emissions proposed for the year 2000 Japanese market was also demonstrated. These results are summarised in this paper and justify the need for a major research programme aimed at demonstrating the full potential of using EGR to develop a fuel efficient, low emission truck engine concept for the 1990's and beyond.

This paper describes latest results from the Ricardo heavy duty diesel engine research programme. Using a Diesel Kiki P-TICS II injection system, matched to a low swirl combustion chamber, emission results well within the US 1991 engineering targets have been achieved with good fuel economy. Very low NOx levels have also been demonstrated whilst maintaining good fuel economy and particulate emissions within the 1991 standards. Analysis of results indicates that injection timing and rate control, as embodied in the P-TICS approach, is a key technology for achieving these low emissions with good fuel economy.

Future emission standards for heavy duty diesel engines will require the application of improved fuel injection systems with high pressure capability and electronic control of timing and fuelling. A recent Ricardo research project has concentrated on the application of the latest in-line pump from Robert Bosch, designated RP39, to a prototype turbocharged and aftercooled heavy duty diesel engine based on the Volvo TD122. The maximum pressure capability of the prototype RP39 used during the experiment was 1400-1500 bar at the injector nozzle. The pump also featured electronic control of the injection timing and rate by the sleeve control principle. The RP39 was matched to a revised low swirl combustion system.

An extensive range of fuels has been evaluated in representative naturally aspirated IDI and DI combustion systems with cylinder sizes of 0.61 and 0.62 litre and rated speeds of 70 and 67 rev/s respectively. Performance, gaseous and particulate emissions and detailed combustion data were obtained, with the objective of correlating combustion and performance parameters with a view towards defining an improved engine-based fuel rating technique. The ASTM D613 procedure was found to not accurately predict the ignition delay for vegetable oil and volatile blends of naphtha and methanol with D2. Petroleum and synthetic derived middle distillates and a vegetable oil ester were ranked correctly. Ignition delay was found to feature in defining cold start, noise and light load HC and CO emissions. A relatively simple rating method measuring ignition delay to rank these parameters is discussed, together with the use of heat release for NOx ranking.