Analysis and Optimisation of the Combustion Process on a Medium-Speed Dual-Fuel Single-Cylinder Research Engine Using Highly Fluctuating Fuel Gas Qualities

The world of shipping is at a turning point. Due to the pressure of public debates, the entire industry is being called upon to become more environmentally friendly and to eventually reach climate neutrality. Shipping associations, ship-owners and large engine manufacturers have recognised this and are increasingly turning to alternative fuels. Alongside methanol, ammonia and other PtL (Power to Liquid) fuels, liquefied natural gas (LNG) offers one way of achieving these goals. Although currently still derived from fossil sources, LNG alone combines the properties of having a very well-developed land-based infrastructure, of enabling 100 % climate-neutral supply via electrolysis and hydrolysis, while offering the possibility to use any high proportion of climate-neutral synLNG as a drop-in fuel during the transformation process.

Up to now, engines in the marine sector, which are often designed according to the dual-fuel principle, have predominantly operated in fixed application areas. It is therefore possible for ships to bunker gas qualities that are as constant as possible at fixed stations and for manufacturers to optimise their engines for a certain gas quality range. This has mostly been achieved by means of specially adapted engine control unit mappings and hardware adjustments to the compression ratio. In the case of a worldwide application with frequently changing bunker locations, this approach has to accept disadvantages in efficiencies and emissions.

This paper characterises the combustion behaviour of medium-speed dual-fuel large engines on the basis of test bench measurements from a single-cylinder research engine operating using strongly fluctuating gas qualities. Engine control unit measures will be presented which enable the engine to operate in a methane number (MN) range from 105 down to 65 without hardware adjustments and without loss of performance. For this purpose, the Chair of Piston Engines and Internal Combustion Engines utilises a gas mixing unit with which the methane number (MN) and heating value (HV) can be adjusted by adding carbon dioxide and propane to the base gas. Adaptations of the pilot fuel injection strategy, especially with regard to injection pressure, quantity and timing, show great potential for reducing engine knock. The relationship between the energy release process in the cylinder and the occurrence of combustion anomalies is illustrated on the basis of combustion process and emission measurements.

This article examines selected experimental results and provides an outlook on further development steps towards an automated adaptation of the combustion process.