Design Development of a Modular Gas-Diesel Retrofit System for Locomotive Engines Without Deep Base Engine Modification

The rapid escalation of diesel fuel costs combined with increasingly stringent emissions regulations compels the railway sector to seek cost-effective alternatives for the existing diesel locomotive fleet. This study analyzes the conceptual and engineering foundations of a modular gas-diesel dual-fuel retrofit system designed to be installed on diesel locomotives without modification of the base engine cylinder head, injectors, or compression ratio. The primary objective is to establish a technically verified design framework for a load-adaptive fuel control system that maintains diesel-pilot ignition while substituting up to 65–70% of the fuel energy with compressed or liquefied natural gas at cruise conditions. A systematic literature review, comparative technical analysis, and engineering case study methodology are applied. The results demonstrate that the proposed modular architecture yields fuel cost reductions of approximately 35–40%, along with verified reductions in NOx emissions by 60–67%, particulate matter by 89–90%, SOx by 95–100%, CO by 50–65%, and CO2 by 22–25% relative to the pure diesel baseline. The findings are applicable to railway operators, locomotive manufacturers, and infrastructure planners engaged in sustainable rail transport transitions