RANS Study on the Impact of Equivalence Ratio on Natural Gas/Diesel-Fueled Combustion in RCCI Engine

Document Type : Research Paper

Authors
Fathi Hamdi
Wassim Harizi
Mouldi Chrigui
University of Gabes, Laboratory of Mechanical Modeling, Energy and Materials (M2EM), National school of engineers of gabes (ENIG), Address, Gabes, 6029, Tunisia
10.22055/jacm.2025.47683.4763
Abstract
The primary reason in favor of Reactivity Controlled Compression Ignition (RCCI) is that combustion occurs at low temperature, leading to low thermal NOx. Using the RCCI approach is highly demanded due to stringent emission laws. The main objective of this paper is to improve engine efficiency and mitigating output pollutants. This paper investigates the impact of equivalence ratio on combustion, pollutants and performances of Natural Gas/Heptane fueled combustion. A numerical model is validated by comparing the experimental results with the numerical data. The adopted equivalence ratios are ф = 0.3, 0.4, 0.5, 0.6, 0.7. For each case, the amount of natural gas is increased while heptane spray remains unchanged. Ansys-forte performs the simulations using RANS framework. The hybrid model Kelvin Helmholtz Rayleigh Taylor governs the spray atomization, though turbulence is pursued using the RNG K-ɛ model. Under an engine regime of 910 rpm, the lowest indicated specific fuel consumption is found at ф = 0.6. It is reduced by around 8% compared to the experiment. Keeping with ф = 0.6, an increase of 15% in temperature compared to experimental work (ф = 0.4). This change in temperature leads to a 6% reduction in CO.  The combination of NG/heptane shows a large reactivity gradient. This reactivity explicitly impacts combustion duration and phasing. 
Keywords
CFD
Natural gas/ heptane
RANS
KH/RT
Equivalence ratio
Subjects

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Journal of Applied and Computational Mechanics
Volume 11, Issue 4
Autumn 2025
Pages 1075-1086