Author(s)

M. Gambino, S. Iannaccone & L. De Simio

Abstract

Mixed fuel (MF) technology was the first way proposed for natural gas (NG) utilization in heavy-duty transportation. The unsolved problems of high levels of unburned hydrocarbons (THC) and the low amount of possible substitution of diesel oil with NG lead to the renouncing of this technology in favour of spark ignited full NG engines. In many situations, mixed fuel could represent the only way to access the environmental benefits connected to NG use in the transport sector. Therefore, a new generation of mixed fuel systems was developed and analysed the effects of intake throttling, catalytic exhaust gases and exhaust gas recycling (EGR). In the present paper, the influence of each component on performance and emissions is evaluated and the results on the regulated test, for a heavy-duty engine, are reported. Keywords: mixed fuel, natural gas, emission reduction. 1 Introduction Since the 1980s, mixed fuel technology was suggested as a realistic way for natural gas utilisation in heavy duty transport circulating in urban areas as an alternative to full natural gas spark ignited engines, not available at that time [1]. Although the unsolved problems of low percentage substitution of diesel oil with NG and high THC emissions, especially at low and medium loads, MF technology has been utilised thanks to the possibility of lowering particulate matter (PM) and exhaust toxicity. The MF technology was particularly suitable to overcome the inconvenience of the high costs of full NG conversion, retaining the possibility of switching to full diesel (FD) operation. In a diesel-NG MF operation, a carburetted air NG mixture enters the cylinder and is ignited by means of pilot diesel oil injection, as in a compression ignition engine. Then the combustion propagates by means of different flame

Keywords

mixed fuel, natural gas, emission reduction.