Effects of port-fuel injected methanol distribution on cylinder-to-cylinder variations in a retrofitted heavy-duty diesel–methanol dual fuel engine

Artikel i vetenskaplig tidskrift, 2025

A 6-cylinder, 13-litre diesel engine was converted to operate on a combination of port-fuel-injected (PFI) methanol and direct-injected (DI) diesel as the pilot fuel. This conversion presents significant challenges, particularly in the design of the inlet manifold, due to inevitable methanol mass imbalances between cylinders that must be minimized. This study integrates experimental and numerical methods to investigate methanol distribution in the retrofitted, non-EGR marine diesel engine. The focus is on cylinder-to-cylinder variations caused by uneven methanol distribution. Two in-cylinder pressure sensors were employed to measure and compare pressure in the second and sixth cylinders. Results indicate that increasing the methanol energy fraction (MEF) at each test point intensifies the differences between the pressure traces in the two cylinders. To delve into this phenomenon, a computational fluid dynamics (CFD) model was developed to explore the behavior of the inlet manifold and the PFI system. Additionally, shadowgraphy experiments were conducted in an optical spray chamber to validate the CFD model. Analysis based on the model suggests that cylinder-to-cylinder variation stems from uneven fuel distribution between cylinders. Calculations reveal that the difference in the mass of methanol across cylinders can reach up to 18% at high MEFs, consistent with experimental findings. Furthermore, a novel design for the inlet manifold was devised and simulated, demonstrating a marked enhancement in fuel distribution. The revised design effectively reduces the fuel mass imbalance to 3%, with the remaining slight imbalance caused by gaseous fuel accumulation at the end of the inlet manifold. Finally, simulations were performed to scrutinize the impact of injection timing, injection duration, and injector location on fuel mass distribution imbalance. The results show that while the manifold design is the most important parameter affecting the fuel distribution, the PFI location and settings can also be adjusted to mitigate the fuel distribution problems.