Experimental Assessment of a Diesel-LPG Dual Fuel Supply System for Retrofit Application in City Busses

Gas-operated vehicles powered by natural gas (NG) or other gaseous fuels such as liquefied petroleum gas (LPG), are seen as a possible option for curbing CO₂ emissions, fuel consumption and operating costs of goods and passenger transport. Initiatives have been adopted by various public organizations in Europe and abroad in order to introduce gas-fueled vehicles in their fleets or use retrofit fueling systems in existing ones. In this study a retrofit dual fuel (diesel-gas) fuelling system was investigated as a potential candidate technology for city bus fleets. The system is marketed under the commercial name d-gid. It is a platform developed by the company Ecomotive Solutions for the control and management of a diesel engine fuelled with a mixture of gaseous fuels. In order to assess its environmental and cost effectiveness the system was tested on a Volvo city bus. The tests were performed on an HDV chassis dyno under various driving conditions. Fuels used were EN590 diesel fuel and EN589 LPG. Regulated pollutant emissions were measured including CO₂, CO. THC, CH₄, non-methane hydrocarbons (NMHC), PM, NO_x and Particle Number. Diesel fuel flow was also recorded. Vehicle simulation was performed using the PHEM simulation software to simulate more realistic operation. Results indicated small differences in exhaust emissions. Benefits were observed for PM and the emission levels of non-methane hydrocarbons were increased. Minor reductions (up to 2%) were observed for CO₂. Under low load conditions the gas fuelling system has only little contribution to engine fuelling. Under medium and high load operating conditions the system manages to substitute part of the conventional diesel with LPG. Simulations indicated that a substitution of diesel fuel with LPG of around 21% is achievable over realistic operation.