Performance Evaluation of Diesel Locomotives Converted to Liquefied Gas Fuel

Background: The decarbonization of non-electrified rail transport requires alternative fuel solutions capable of reducing diesel-fuel consumption while maintaining the operational capabilities of existing propulsion systems. Dual-fuel operation on liquefied natural gas (LNG) offers a potential upgrade path for existing diesel locomotives, especially where full electrification is not currently possible. Objective: This study evaluates the technical, operational, and economic feasibility of converting a TEM2 shunting locomotive equipped with a PD1M diesel engine to LNG-based dual-fuel operation while retaining diesel fuel as a pilot fuel. Methods: A computational and analytical approach was used to evaluate the fuel and energy balance, LNG and pilot-diesel consumption, fuel-substitution scenarios, economic performance, and the influence of additional LNG equipment on locomotive mass distribution. The main and alternative LNG consumption scenarios were considered to assess the sensitivity of economic outcomes to fuel consumption assumptions. Results: The baseline diesel consumption of the TEM2 locomotive was approximately 428 kg/day, compared with a calculated pilot-diesel consumption of 42.8 kg/day under dual-fuel operation. The primary technical calculation resulted in an LNG consumption of approximately 350 kg/day. Under the base economic scenario, the estimated annual fuel-cost saving was approximately 2.95 million KZT per locomotive, based on a reference conversion investment of approximately 9.91 million KZT and a simple payback period of approximately 3.36 years. However, an alternative LNG-consumption scenario of 385.2 kg/day resulted in a negative annual fuel-cost effect of approximately 2.43 million KZT, demonstrating the sensitivity of the economic outcome to LNG consumption and relative fuel prices. The mass-distribution analysis showed agreement with reference locomotive data within approximately ±3%, while the calculated installation of additional gas-fuel equipment shifted the center of gravity by approximately 480 mm. Conclusions: The results demonstrate the potential technical feasibility of the proposed LNG diesel-fuel upgrade and identify fuel consumption conditions under which economic benefits can be achieved. The economic outcome is highly dependent on actual LNG consumption, relative fuel prices, and operating conditions. The analysis also highlights the importance of fuel system integration, mass distribution, low-load operation, and combustion stability in adapting existing diesel propulsion systems to dual-fuel LNG operation. Full-scale pilot studies are needed to confirm fuel consumption and combustion performance, quantify emissions including methane breakthrough, and assess long-term operational reliability under representative railway operating conditions.