Premixed mixture ignition in the end-gas region (PREMIER) combustion in a natural gas dual-fuel engine: operating range and exhaust emissions

Abstract

This paper is concerned with engine experiments and spectroscopic analysis of premixed mixture ignition in the end-gas region (PREMIER) combustion in a pilot fuel ignited, natural gas dual-fuel engine. The results reveal the characteristics and operating parameters that induce and affect this combustion mode. The PREMIER combustion is followed by natural gas flame propagation. Pilot-injected diesel fuel ignites the natural gas/air mixture, and the flame propagates before the natural gas/air mixture is autoignited in the end-gas region. This combustion cycle differs from a knocking cycle in terms of combustion and emission characteristics. The PREMIER combustion can be controlled by pilot fuel injection timing, the equivalence ratio, and the exhaust gas recirculation (EGR) rate, and can be used as an effective method for high load extension on a dual-fuel engine. An analysis of the relationship between the maximum in-cylinder pressure and its crank angle (CA) is used to compare combustion dynamics during conventional, PREMIER, and knocking combustion. In PREMIER combustion, the heat release gradually transforms from the slower first-stage flame rate to the faster second-stage rate. During PREMIER combustion, the maximum indicated mean effective pressure (IMEP) and thermal efficiency increase by about 25 per cent compared with those of conventional combustion, and low carbon monoxide (CO) and total hydrocarbon (HC) emissions can be achieved. However, nitrogen oxide (NOx) emissions increase. Spectroscopic analysis shows that the intensity of the OH* emissions in the end-gas region increases as the combustion mode transforms from conventional to PREMIER to knocking. In all three modes, emission fluctuations above 650 nm can be observed in the end-gas region. These emissions are attributed to the luminosity from soot particles formed during the concurrent diesel fuel combustion.

Dual-Fuel Combustion Characterization on Lean Conditions and High Loads

“…A possible additional attribute in DF-combustion was later discovered by Azimov et al [17,18]. According to this study, an additional possible component of heat release could be achieved: a bulk ignition of the end gas region.…”

“…The rapid methane combustion in the end gas region causes a high HRR-peak in the later part of the DF-combustion. Based on the HRR, a rapid heat release phase originating from bulk ignition in the end gas region can be seen [17]. The bulk ignition starts in the 368 degree region forming a rapid HRR caused by the simultaneous combustion of the end gas.…”

Simulation Analysis of Combustion Parameters and Emission Characteristics of CNG Fueled HCCI Engine

“…The timing of autoignition of HCCI combustion is determined by the cylinder charge conditions, rather than the spark timing or the fuel injection timing that are used to initiate combustion in the SI and CI engines, respectively [3]. As demonstrated by many experimental results [4,5], controlled autoignition requires regulation of the charge properties, namely, temperature, pressure, and composition at the intake valve closing [IVC]. The numerical approach has significant potential to investigate the HCCI engine combustion phasing, start of combustion (SOC), and emission characteristics [6][7][8].…”

Combustion and Exhaust Emission Characteristics of Diesel Micro-Pilot Ignited Dual-Fuel Engine

“…The details of FFT analysis are given in [35]. Unlike during knocking in traditional sparkignition engines, high frequency oscillations of in-cylinder pressure and knock-sensor signals were not observed during the PREMIER combustion mode.…”