Search Results

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.

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.