Combustion performance and stability of a dual-fuel diesel–natural-gas engine

Abstract

Experimental investigations on the combustion performance and the stability of a dual-fuel engine fuelled with diesel and natural gas were conducted. The effects of the pilot diesel quantity and the pilot diesel injection timing were analysed. The results show that the maximum (peak) in-cylinder pressure increases and appears earlier with increasing pilot diesel quantity. The heat release rate has two peaks during the process of combustion. Earlier pilot diesel injection resulted in an earlier pressure evolution and a higher peak in-cylinder pressure. Correspondingly, the ignition of the pilot diesel was advanced and the heat release rate of diesel ignition increases. Earlier diesel injection timing increases the diesel combustion heat release, and the combustion of the whole charge in cylinder is more drastic. The pilot diesel quantities have different effects on the cycle-by-cycle variations (i.e. the coefficient of variation). At a low load, both very high and very low pilot diesel quantities lead to a high coefficient of variation in the indicated mean effective pressure, and the effect becomes weaker with increasing load. The coefficient of variation in the indicated mean effective pressure decreases and the coefficient of variation in the the peak in-cylinder pressure increases with increasing load. Additionally, the coefficient of variation in the indicated mean effective pressure decreases as the pilot diesel injection was advanced. The largest value of the coefficient of variation in the peak in-cylinder pressure occurs at 20° crank angle before top dead centre. The maximum rate of pressure rise increases dramatically with earlier pilot diesel injection timing. Nitrogen oxide emissions increase and hydrocarbon emissions decrease with increasing pilot diesel quantity. The hydrocarbon emissions decrease at earlier diesel injection timing; however, the nitrogen oxide emissions increase.

Experimental investigation on performance and heat release analysis of a pilot ignited direct injection natural gas engine

“…11 that the start of diesel combustion is advanced and the first peak values of pressure rise rate and second derivation of in-cylinder pressure during pilot diesel combustion process are raised with the increase of diesel injection pulse width as a consequence of earlier start of diesel injection and increased pilot diesel quantity. This result is in good agreement with that available in the study on a pilot ignited premixed natural gas engine of Sun et al [26]. Moreover, it can also be observed that the maximum values of in-cylinder pressure, maximum pressure rise rate as well as second derivation of in-cylinder pressure reduce with increasing diesel injection pulse width when diesel injection pulse width varies from 0.3 ms to 0.7 ms, while increase slightly when diesel injection pulse width extends from 0.25 ms to 0.3 ms.…”

“…Moreover, it can also be observed that the maximum values of in-cylinder pressure, maximum pressure rise rate as well as second derivation of in-cylinder pressure reduce with increasing diesel injection pulse width when diesel injection pulse width varies from 0.3 ms to 0.7 ms, while increase slightly when diesel injection pulse width extends from 0.25 ms to 0.3 ms. This, however, is inconsistent with that reported in an investigation on conventional dual fuel engine [26], where the natural gas is premixed before inducted into the cylinder and, consequently, the mixing quality of natural gas is independent of the ignition delay. For direct injection natural gas engine studied in the present work, the formation of combustible mixture is highly dependent on the ignition process because natural gas is directly injected into the cylinder, thus, the time available for mixture formation is quite limited.…”

Optical Investigation of Sooting Propensity of n-Dodecane Pilot/Lean-Premixed Methane Dual-Fuel Combustion in a Rapid Compression-Expansion Machine

“…Gradients of soot temperature along the line of sight result in underprediction of the soot KL value [42] due to the T 4 dependence of the total black body luminosity. According to the Wien's law, in the short wavelength range this dependency is even stronger (T [5][6][7][8][9][10][11][12][13][14][15] ). This strongly biases the multi-color detection of T s-app towards hottest soot layers along the line of sight.…”

“…Various aspects of dual-fuel combustion (Diesel pilot ignited) have been studied up to date in complete engines [5][6][7], single cylinder engines [8][9][10][11][12][13][14][15], optical engines [15][16][17][18] as well as rapid compression machines [19][20][21]. The approach of most of the engine experiments was to substitute part of the Diesel fuel (by reducing the injection duration) with premixed methane while monitoring the exhaust emissions and heat release rate.…”

“…The approach of most of the engine experiments was to substitute part of the Diesel fuel (by reducing the injection duration) with premixed methane while monitoring the exhaust emissions and heat release rate. Significant reduction of the engine NO x emissions at low and moderate loads has been reported together with reduced peak pressure rise and prolonged combustion duration [5,6,[8][9][10][11][12]. The drawback of the dual-fuel engines (in gas mode) is most obviously a significant increase of the UHC emissions which are more than two orders of magnitude higher than when engine runs in Diesel mode [8,11,12].…”