Search Results

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.

A research programme has been carried out to investigate the fuel economy potential of a number of engine concepts both on the testbed and in a vehicle. A 1.5 litre high compression ratio engine with a High Ratio Compact Chamber (HRCC) and a mechanically supercharged 1.3 litre engine were compared with a conventional 1.6 litre engine. Each of the engines was developed on European Premium (97 RON) fuel to have the same torque curve shape and to meet the European ECE 15-04 emissions standard when fitted to a 910 kg vehicle. The results showed the HRCC engine concept to reduce fuel consumption by 10% and the supercharged engine by 3% compared to the conventional engine on the basis of equal fuel quality requirement.

The use of high ratio compact combustion chambers in gasoline engines has been investigated. The objectives of the research are improved fuel economy within a given set of exhaust emission constraints. The effects of a number of parameters such as swirl, compression ratio and combustion chamber geometry have been investigated, and the conclusions are that for Europe, 13:1 compression ratio is feasible and should yield 10% better fuel economy in passenger cars, while for the USA and Japan, 11:1 compression ratio is preferable, and should yield about 5% better fuel economy.

This study investigates the causes for tailpipe mixture strength excursions during transient operation of an electronically controlled, central fuel injected engine. The investigation was made using a Ford 5.0L V8 engine instrumented to enable continuous monitoring of the tailpipe air-fuel ratio. Transient excursions of up to 20% are observed under warm engine conditions. Two causes of the excursions were identified: system time delays and fuel droplet deposition on induction system surfaces. A programmable control strategy was developed to compensate for observed lean excursions during accelerations. This was done by modifying the injector signal to provide the necessary fuel enrichment. Transient requirements were optimized across a range of engine operations. The results have been summarized in two sets of curves-one defining the enrichment fuel volume and the other specifying the form of enrichment fuel supply.

A research programme has been carried out to investigate the effects of operating gasoline engines with different combustion systems. The results showed that at high compression ratios (13:1) compact combustion chambers allowed an increase in compression ratio of between 1 and 2½ numbers for a given fuel quality compared to conventional designs. Fuel economy benefits of about 10% could be achieved by using high ratio compact chambers and lean operation.