A wide investigation on the emissions of a heavy-duty engine fuelled respectively by CNG and LNG under World Harmonized Transient Cycle

Natural gas (NG) is an important fuel in combustion/thermal field, CNG (compressed natural gas) and LNG (liquefied natural gas) are two common application modes in internal combustion engines, debate between the two continues. To clarify that, the investigation must be carried out on a same engine and under same conditions. This was done in the current study under transient operations. Totally eight cases were tested with consideration of raw/tailpipe emissions under cold/hot starts, main findings include: (1) Fuel consumption of LNG is higher than that of CNG by 16.8 % under cold start. The worst case is LNG under cold status, CNG does not have this problem. (2) Another evidence for the deteriorative combustion of LNG under cold start is that the ratio of CO 2 /brake specific fuel consumption (BSFC) is ∼2.1, but under other cases it is within range of 2.6–2.7 which is lower than diesel engines, so it is a low carbon way by changing from oil to gas. (3) LNG generates the most PM (particulate matter) under cold start cycle which is still lower by 1–2 orders of magnitude than a diesel/NG dual fuel engine. The maximal PN (particle number) is only 5.78E+ 10 #/s of LNG under cold start, while it is 2.69E+ 11 #/s for CNG under hot start, but for PM the former outweighs the latter. So under poor combustion, more substances are attached to particulates, leading to PM growth, thus the diameters are bigger. (4) The CH 4 conversion efficiency by three way catalyst (TWC) is 88.6 % under CNG cold start cycle due to lower coolant inlet temperature, that of all other cases are above 95 %. CNG/LNG application comparison to a heavy-duty engine was fairly clarified by comprehensive parameter measurement. So, this study is anticipated to provide a nice implication for better applications of NG fuels in combustion field.