An Optical Characterization of Dual-Fuel Combustion in a Heavy-Duty Diesel Engine

Abstract

Dual fuel (DF) combustion technology as a feasible approach controlling engine-out emissions facilitates the concept of fuel flexibility in diesel engines. The abundance of natural gas (90-95% methane) and its relatively low-price and the clean-burning characteristic has attracted the interest of engine manufacturers. Moreover, with the low C/H ratio and very low sooting tendency of methane combined with high engine efficiency, makes it a viable primary fuel for diesel engines. However, the fundamental knowledge on in-cylinder combustion phenomena still remains limited and needs to be studied for further advances in the research on DF technology. The objective of this study is to investigate the ignition delay with the effect of, 1) methane equivalence ratio, 2) intake air temperature and 3) pilot ratio on the diesel-methane DFcombustion. Combustion phenomenon was visualized in a single cylinder heavy-duty diesel engine modified for DF operations with an optical access. The high-speed natural luminosity (NL) imaging technique was employed to record the temporally resolved incylinder combustion event at an operating load of approx. 10 bar IMEP at 1400 rpm. The results show that flame propagation becomes stable and sustained with an increase in either of the methane equivalence ratio, intake air temperature, or diesel amount. However, the sensitivity of each effect on the flame propagation and ignition delay was observed to be different. The effect of these parameters on DF combustion has been characterized with the help of NL images and corresponding cylinder pressure and net heat-release rate (HRR) data. The study also presents a detailed discussion on the analyzed ignition delay trends.

Dual-Fuel Combustion

“…Since dual-fuel engines have a fuel that is port-injected and one that is direct-injected, they often exhibit a twostage combustion process. The portion of combustion that occurs in a premixed vs. a diffusion mode will be strongly dependent on the amount of each fuel that is used [39]. While this makes the combustion process more complicated, dual-fuel injection can provide stable combustion of a less reactive fuel like natural gas in CI engines.…”

Comparative study on chemical kinetic schemes for dual-fuel combustion of n-dodecane/methane blends

“…review by Karim [41]). Most of the recent DF combustion literature is still based on laboratory engine experiments and target on performance, efficiency and combustion stability issues [20,27,[41][42][43][44][45][46], lacking details on ignition and premixed flame initiation. In contrast, such features are identified and well documented in high-fidelity experiments for diesel spray combustion [47][48][49].…”

“…As briefly discussed earlier, most of the recent DF combustion studies are related to experimental works on performance, efficiency and combustion stability issues in laboratory engines with the following observations: 1) The IDT of a diesel spray increases with increasing ambient methane concentration [41,43,46,70].…”

“…Some DF engine experiments utilize simple optical diagnostics to obtain information on ignition and flame initiation [46,[72][73][74][75][76]. As illustrated in Fig.…”

“…2.2, spatial and temporal resolutions in most optical engine systems are rather limited and combustion dynamics is influenced by swirl and walls, leading to often qualitative conclusions. Figures are obtained from the work by Ahmad et al [46] and were utilized in Publication III as well.…”