Development of a simplified n-heptane/methane model for high-pressure direct-injection natural gas marine engines

Abstract

High-pressure direct-injection (HPDI) of natural gas is one of the most promising solutions for the future ship engines, for which the combustion process is mainly controlled by the chemical kinetics. However, the employment of detail chemical mechanisms for the multi-dimensional combustion simulation is significantly expensive due to the large scale of the marine engine. In the present study, a reduced n-heptane/methane mechanism consisted of 35-step reactions was constructed using multiple reduction approaches. Then this mechanism was further reduced to include only 27 reactions by the HyChem (Hybrid Chemistry) method. An overall good agreement with the experimentally measured ignition delay data of both nheptane and methane for these two reduced mechanisms was achieved and reasonable predictions for the measured laminar flame speeds were obtained for the 35-step mechanism. But the 27-step mechanism cannot predict the laminar flame speed very well. In addition, these two reduced mechanisms were both able to reproduce the experimentally measured in-cylinder pressure and heat release rate profiles for a HPDI natural gas marine engine, although the engine-out CO emission was overpredicted and the NOx emission was slightly underestimated. The predicted distributions of temperature and equivalence ratio by the 35-step and 27-step mechanisms are similar with those of the 334-step mechanism. However, the predicted distributions of OH and CH2O are significantly different from those of the 334-step mechanism. In short, the developed reduced chemical kinetic mechanisms provide a high-efficient and dependable method to simulate the characteristics of combustion and emissions in HPDI natural gas marine engines.

A Mapping Approach for Efficient CFD Simulation of Low-Speed Large-Bore Marine Engine with Pre-Chamber and Dual-Fuel Operation

“…The physical and chemical properties of diesel are approximated as those of n-dodecane and n-heptane, respectively, and the natural gas is approximated as methane. For WSR model, a reduced chemical kinetic mechanism of methane/n-heptane with 79 species and 262 reactions [24] was employed to simulate the natural-gas/diesel dual-fuel combustion. This chemical mechanism was validated for both methane and n-heptane combustion experiments and showed quite good agreement with the experiments in terms of laminar flame speed and ignition delay.…”

A Numerical Study of the Effects of Using Reformer Gas on Ignition Characteristics under Dual-Fuel Engine-Relevant Conditions

“…Although many works of literature on diesel and NG dual-fuel combustion have been published including the zero-dimensional model [25,26] and the three-dimensional spray study [27,28], however, previous studies mainly focused on the ignition characteristics of diesel and NG mixture when diesel is injected into NG. ere is still an obvious gap in understanding the ignition and flame characteristics of H 2 and CO additives in different combinations of dual-fuel blends.…”

Investigation of the Combustion Kinetics Process in a High-Pressure Direct Injection Natural Gas Marine Engine

“…A promising NG operating mode is fueled with diesel/NG dual fuel, in which the low-reactivity NG is supplied as the primary energy source, whereas of the high-reactivity diesel is supplied as the ignition source, which is directly injected into the combustion chamber. 2,3 The NG dual fuel engines can be roughly categorized into the low-pressure dual fuel (LPDF) engine and high-pressure direct injection (HPDI) engine. 4 For LPDF engines, NG is mixed with air outside the cylinder or injected into the cylinder relatively early, which is then primarily consumed during the premixed-combustion process.…”

“…Natural gas (NG) is a promising alternative fuel for engine combustion owing to its abundant resources and low pollutant emissions. , Due to the long ignition delay and high autoignition temperature, NG engine requires additional energy or ignition source to ignite. A promising NG operating mode is fueled with diesel/NG dual fuel, in which the low-reactivity NG is supplied as the primary energy source, whereas of the high-reactivity diesel is supplied as the ignition source, which is directly injected into the combustion chamber. , …”