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One of the possible solutions in order to reduce NOX and PM emissions and fuel specific consumption in a diesel engine is to substitute a part of the diesel oil with a gaseous fuel. Natural gas, due to the high octane number, allows such substitution without great modifications to the original engine, just introducing the gas feeding system. The utilization of natural gas (usually referred as “alternative fuel”) instead of oil is an important advantage of such technology in terms of energy sources. In this paper the conversion of the IVECO 8360.46R engine, for bus applications, to dual-fuel operations is discussed. Experimental tests were performed to define the general behaviour of the engine, especially at partial loads. Main target of the present study was the analysis of engine requirements to maintain the same output load as the full-diesel operation, and controlling exhaust emissions.

The use of Compressed Natural Gas as an alternative fuel in urban transportation is nearly established and represents an efficient short and medium term solution to face with urban air pollution. However, in order to completely exploit its potential, the engine needs to be specifically designed to operate with this fuel. In the latest years, the authors have investigated the performances of a Heavy Duty Turbocharged CNG fuelled engine both experimentally and by using some analytical tools specifically developed by them which have been used for the engine optimisation. In the present paper the simulation approach has been enlarged by means of a co-operative use of a CFD code and experimental analysis on the actual engine. The numerical simulation of combustion process has, in fact, been used, to interpret series of pressure cycles, aiming to analyse how cyclic fluctuations influence engine behaviour in terms of combustion efficiency and temperature and pollutant distribution.