Abstract
The present study is a continuation of the previous work by Ahmad et al. (2020), in which ethane (C2H6) enriched diesel-methane (CH4) dual-fuel (DF) combustion was experimentally investigated in a single-cylinder heavy-duty engine. Here, the experiments of ethane enriched DF combustion are carried out with new details together with supporting zero-dimensional (0D) and one-dimensional (1D) chemical kinetics simulations. Three port-fuel injected (PFI) gaseous blends of pure methane with varying ethane concentrations of 0%, 10%, and 20% are used as the main fuels. The PFI gaseous blend provides 97% of the total-fuel energy (TFE), which is ignited by a small 3% (TFE based) pilot diesel. Experiments are performed under lean condition (∅gas = 0.52) for two engine speeds while keeping the TFE and other operating conditions constant. Calculated results from 0D and 1D simulations under engine relevant conditions including theoretical combustion mode analysis (β-curve) are used to deepen the phenomenological understanding of the experimental results. The results reveal that adding ethane into pure methane has minor effects on the pilot-diesel ignition timing. However, ethane addition greatly enhances the ignitability of methane after the start of combustion. Ethane enriched gaseous blends yield higher thermal efficiency and reduce combustion duration compared to pure methane. According to combustion mode analysis, ethane tendency to promote spontaneous autoignition may be one of the reasons for improving overall combustion performance. It is observed that ethane enriched gaseous blends produce lower unburned methane (UB-CH4) and unburned hydrocarbons (THC) accompanied with higher nitrogen oxides (NOx) because of the higher combustion efficiency. Furthermore, ethane addition considerably helps to reduce cycle-to-cycle variations under lean conditions compared to pure methane.
Highlights
Natural gas (NG) as a low-carbon gaseous fuel is potentially a feasible alternative fuel for use in internal combustion engines, especially in diesel engines to meet stringent emission regulations [1,2,3]
In the following, to aid with inter pretation of the combustion process, combustion stages are distin guished from similar heat release rate (HRR) profiles according to Fig. 2 (Section 2.5)
It is observed that ethane enrichment has less significant effect on pilot diesel in reducing ignition-delay time at both engine speeds, it enhances the ignitability of pure methane
Summary
Natural gas (NG) as a low-carbon gaseous fuel is potentially a feasible alternative fuel for use in internal combustion engines, especially in diesel engines to meet stringent emission regulations [1,2,3] It is mainly composed of methane (CH4) along with other heavier alkanes such as ethane (C2H6) and propane (C3H8) as well as diluents (N2 and CO2). Methane is a clean burning fuel, which produces low greenhouse gas (GHG) emissions due to its low C/H ratio [4] It is still a fossil fuel like diesel and gasoline, which may restrict its consumption considering the future GHG goals in transport sector. Efficient burning of pure methane in diesel engines is another challenge due to its high autoignition energy requirement [6,7]
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