SAE 892137

Performance and Cyclic Variability of Natural Gas Fuelled Heavy Duty Engines

Garcia, P.; Shiells, W.: Transport Fuel Systems (NZ) Limited

Chanchaona, S.; McFeaters, J.S.; Raine, R.R.: University of Aucland


Two heavy duty turbocharged and aftercooled diesel engines have been converted to Spark Ignition (SI) for natural gas fuelling. One engine features two valves per cylinder, high primary swirl and a compact combustion chamber. The other engine has four valves per cylinder and a more open combustion chamber shape. Both engines were characterised on a dynamometer and subsequently put into service where one of the engines has been monitored extensively.

When a diesel engine is converted to SI operation, there is an involved process which must be carried out to ensure reliable and efficient operation. Many aspects of the conversion process are limited by the original configuration of the diesel engine. Some of these aspects, such as combustion chamber shape, are shown to be important to the optimisation of an SI converted engine and are highlighted in the comparison of these two engines.

The conversion process, dynamometer testing and optimisation required to bring these engines into reliable fleet service are presented in this paper.

TECHNIQUES for the retrofit conversion of diesel engines to alternative fuels use have been developed by Transport Fuel Systems (NZ) Limited. This initially took the form of developing conversion systems to allow dual-fuel operation using gaseous fuels; more recently the emphasis has shifted to retrofits of diesel engines to spark ignition and optimisation using an alternative fuel. A substantial part of the development work has been carried out in conjunction with the Vehicle Fuels and Research Unit of the University of Auckland. A list of engines for which either dual-fuel or SI conversions have been developed is appended to the paper (Appendix A). The technology for these conversions is now commercially available for a number of different engines.

This paper will present results arising from dynamometer testing of two SI engines. The first of these, a Renault MIPS turbocharged and aftercooled engine of 9.8 litres capacity, features a two valve per cylinder configuration and in its diesel form for the intended application in a city bus, realises a maximum power of 167kW. The other engine is a Mack E6-350 4VH turbocharged and aftercooled engine of 10.5 litres capacity, which features four valves per cylinder and is rated at up to 261kW power. Preliminary results from early testing of these engines have been presented elsewhere, (1). Particular reference is made in this paper to work involving cycle-to-cycle variations in cylinder pressure. Also presented are outcomes of field experience, as indicated by on-board data logging for one engine in commercial service (the Mack E6).