Session: 03-03 Advanced Compression Ignition Combustion Strategies

Paper Number: 191113

191113 - Ignition and Early-Stage Spray-Flame Mechanism of Renewable Diesel/Methanol Dual-Fuel Combustion 

Abstract: 

Internal combustion engines (ICEs) can be operated on alternative fuels, such as Renewable Diesel (RD) and methanol (MeOH), to support defossilization. RD and MeOH have very different fuel properties compared to diesel. For example, RD has a higher cetane number (CN) and almost no aromatic content compared to diesel. MeOH has a very low ignition propensity, but its combustion is usually locally leaner thanks to its high volatility and low A/F ratio. This study presents a combination of renewable diesel methanol dual fuel (RMDF) using zero-dimensional (0D) and three-dimensional (3D) computational fluid dynamics (CFD) simulations. Experimental data used for model validation were obtained from single-cylinder engine testing with a compression ratio of 17:1. MeOH fuel was port-injected at the intake port, and RD was directly injected using a stock diesel injector.

Ignition in dual-fuel combustion can be affected by the MeOH substitution rate and the RD injection timing. The 0D ignition delay model shows the kinetic mechanism of the MeOH+RD mixture, where the mixture's reactivity increases (shorter ignition delay) with the addition of methanol under high-temperature (>1050K) conditions. At lower temperatures, the ignition delay increased with increasing MeOH substitution ratio.

The present CFD analysis investigates early-stage reactions in the RMDF mixture that lead to an initial high-temperature ignition event. Combustion behavior was characterized by tracking CH₂O, OH, and HO₂ to capture cool-flame, high-temperature, and fuel oxidation processes, respectively. Results suggest a complex in-cylinder phenomenon between the probability of MeOH auto-ignition and the interaction between the RD spray flame and MeOH in the ambient surroundings.

However, it was shown that the combination of a higher MeOH substitution rate (80% by energy) with a late RD pilot results in a very high maximum pressure rise rate (MPRR), resembling HCCI combustion. It was found that the MPRR can be reduced by a more advanced pilot injection of RD (20° bTDC or earlier). The lower substitution rates of dual fuel results (20% and 50% by energy) have been validated with experimental data. This paper provides an initial understanding of the RMDF ignition mechanism that can achieve a high MeOH substitution ratio, thereby reducing soot and nitrogen oxides (NO_X) emissions through lean combustion of a premixed charge, while maintaining reasonable MPRR.

Presenting Author: Cyrus Bourg Southwest Research Institute

Presenting Author Biography: Mr. Bourg is an engineer from the Powertrain Analysis group in the Powertrain Engineering division at Southwest Research Institute. His work focuses on combustion CFD of internal combustion engines, providing advanced modeling and advanced combustion support for multiple programs at SwRI including the CHEDE-9 consortium.
Mr. Bourg earned his B.S. in Mechanical Engineering from the University of Texas at San Antonio in 2023 and is currently pursuing a master’s in the same field where his research includes CFD with an emphasis on pressure gain combustion.

Authors:

Cyrus Bourg Southwest Research Institute
Khanh Cung Southwest Research Institute
Zainal Abidin Southwest Research Insitute
Thomas Briggs Southwest Research Institute