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In the frame of the IEA-AMF, Annex XVII project ‘Real Impact of New Technologies for Heavy Duty Vehicles’, three state-of-the-art city bus technologies were evaluated for fuel consumption and emissions in real city traffic and in a number of test cycles, both on engine and on vehicle level. One of the three buses was a natural gas bus with multi-point fuel injection, stoichiometric fuel control and three-way catalyst. Compared to the other tested technologies, this engine reached very low exhaust gas emissions. The paper will discuss the results obtained with the stoichiometric natural gas engine and compare the emissions in real traffic versus various engine test cycles, based on a number of influencing parameters. Concerning cycle characteristics it was the distribution of the engine operating points which had most effect on the exhaust gas emissions.

Natural gas has a favorable effect on both the engine performance and emissions. The heavy duty vehicles fueled with natural gas have very low emission levels, not easily obtainable with other fuels, and therefore they are considered the most practicable EEV (Enhanced Environmental Friendly Vehicles). Moreover, the assessment of fuel availability makes its use possible for a long time, whilst the new generation of feeding systems offers solutions to the problem of fuel composition variability. Nevertheless, the positive environmental aspects often are not totally known by people involved in natural gas application, therefore some limitations in the diffusion of this fuel in the transportation sector still appear. This paper refers about the activities, under development at the Istituto Motori, aimed to evaluate the toxicity of engine exhausts gas, based on the analysis of components harmful to human health, such as the carbonyl compounds, PAHs and particulate matter.