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The performance and emissions of a medium duty, turbocharged and aftercooled diesel engine fitted with both standard pistons and experimental pistons have been compared. The experimental pistons incorporated micro-chambers equi-spaced around the periphery of the bowl, connected to the bowl by drilled passages. The tests were run using an “A-B-A” design at three engine speeds over the load range. The paper will report that the experimental pistons have a potential for significant soot reduction without an increase in NOx emissions and with similar fuel consumption. Based on an analysis of the jet flow into and out of the micro-chambers, a possible mechanism for the soot reduction is proposed. The mechanism has been investigated further using VECTIS computational fluid dynamics (CFD) analysis.

Within Europe, agreed EEC Directives now exist to control exhaust emissions from heavy duty truck engines. An agreed EEC directive requires that emissions are reduced in two stages, Euro I and Euro II in accordance with current state-of-the-art developments in technology. Euro I standards were implemented in 1992/93 and Euro II standards will be in place for 1995/96. A third step, Euro III is now envisaged for introduction around the 1999 model year. In this paper, results from research work are presented showing how, with an advanced, heavy duty diesel engine, featuring 4 valves per cylinder and a very high pressure, electronic unit injector, effective control of NOx is possible using exhaust gas recirculation (EGR). After optimising the combustion system and air-fuel ratio with EGR, the test data obtained allow the limits for achievable emissions to be explored.

When developing diesel fuel formulations, it is important to ensure that existing engines in the market place start and continue to run satisfactorily at low temperatures. The objective of this project, carried out jointly by Statoil and Ricardo Consulting Engineers Ltd, was to develop a test technique capable of discriminating between different fuels and to apply the technique to a range of experimental fuels tested in six diesel engines. The engines were selected to represent the technologies available in the current vehicle parc, ranging from indirect injection diesel engines used in passenger cars to highly-rated, direct injection engines found in commercial vehicles. These engines were instrumented to measure crankshaft position and speed, in-cylinder pressure and exhaust emissions. Cold start testing was carried out at -16°C and -24°C in Ricardo's cold chamber and data were recorded during the cold starts by analogue recorders and a high speed digital data logger.

This paper describes the first phase of a project to develop a medium duty engine to run on compressed natural gas (CNG) as an alternative fuel for vehicles such as school buses and medium trucks. The engine uses a lean burn, open chamber design featuring the Nebula combustion system. Mechanical air-fuel ratio control and a mapped high energy ignition system, combined with a wastegated turbocharger, will contribute to the low emissions. The CNG engine will have the maximum commonality with the existing diesel engine and will use the same production tooling wherever possible. The initial build of CNG engine is intended to avoid the expense and complication of an intercooler and catalyst. Future potential for even lower emissions and higher pressure could be achieved by the use of electronic air-fuel ratio control and the addition of intercooling and an oxidation catalyst.