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It is well known that accurate EGR control is paramount to controlling engine out emissions during steady state and transient operation of a diesel engine. The direct measurement of EGR is however non-trivial and especially difficult in engines with no external EGR control where the intake manifold CO2 levels can be measured more readily. This work studies the EGR behaviour in a medium duty diesel engine with a passive EGR rebreathing strategy for steady state and transient operation. High speed (response time ∼1ms) in-cylinder sampling using modified GDI valves is coupled with high frequency response analysers to measure the cyclic in-cylinder CO2, from which the EGR rate is deduced. It was found that controlling the EGR using the passive rebreathing strategy during certain combined speed and load transients is challenging, causing high smoke and NO emissions.

A slipstream of exhaust from a Caterpillar 3126B engine was diverted into a plasma-catalytic NOx control system in the space velocity range of 7,000 to 100,000 hr-1. The stream was first fed through a non-thermal plasma that was formed in a coaxial cylinder dielectric barrier discharge reactor. Plasma treated gas was then passed over a catalyst bed held at constant temperature in the range of 573 to 773 K. Catalysts examined consisted of γ-alumina, indium-doped γ-alumina, and silver-doped γ-alumina. Road and rated load conditions resulted in engine out NOx levels of 250 - 600 ppm. The effects of hydrocarbon level, catalyst temperature, and space velocity are discussed where propene and in one case ultra-low sulfur diesel fuel (late cycle injection) were the reducing agents used for NOx reduction. Results showed NOx reduction in the range of 25 - 97% depending on engine operating conditions and management of the catalyst and slipstream conditions.

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.

The US 1991 and 1994 emission standards for heavy duty diesel engines present the industry with one of the most difficult challenges to date. Achieving the 1994 standards in particular will require extensive development using an integrated approach. All aspects of the engine will need to be addressed including the boost strategy, the combustion system, oil control and exhaust aftertreatment. Engines will need to be fully optimised for transient operation. In this paper, the 1994 technology requirements for highly rated, heavy duty diesel engine's are reviewed.