In India, , as per mandate of hon'ble Supreme Court of India for reduction of emission due to vehicles, compressed natural gas (CNG) powered city buses and passengers cars are in use since 2000. Their usage is limited to metropolitan cities like Delhi, Mumbai, Bangalore etc. due to limitation of CNG storage and dispensing infrastructure along with low energy density storage. High energy density liquid form of natural gas storage (LNG) can overcome these difficulties and promising in near future. Simultaneously, there is a need for development of efficient fuel storage system, fuel supply system, engine optimization & calibration, engine lubricant etc. suitable for implementation of LNG for automotive application. In this background, the present work is aimed at the framework of engine testing facility, development of dedicated lubricant and performance of the engine for LNG application.
This paper describes LNG engine test lab standard operating procedure developed during the LNG internal combustion engine dynamometer testing programme. Due to safety requirement, it is neither advisable nor permissible to connect large LNG cryogenic tankers to engine test bench. Hence, state of the art small & portable cryogenic LNG tank (450 Lit water capacity (WC)) comprised of vacuum and super insulated layered configuration manufactured as per International Organization for Standardization (ISO) 21029-1 and type tested according to ISO-12991 was designed as horizontal tank to transport LNG from large LNG cryogenic tanker to engine testing site. Bharat Stage (BS) VI emission standard complied LNG engine testing facility was developed and forced convection heat transfer methodology applied for avoiding icing at re-gasified liquefied natural gas (RLNG) fuel line.
This paper presents the development of dedicated lubricant for LNG fuelled heavy duty (HD) engine and establishment of oil drain interval and evaluation was done on 6-cylinder HD engine using LNG fuel. The engine was optimized for using LNG fuel. Initial performance of the engine using LNG was compared vis-à-vis CNG and, thereafter, the engine was subjected to endurance test of 1500 hours as per engine simulated driving cycle that closely represents road drive conditions to validate the technology and to establish the drain interval of lubricant. Further, to access the actual performance, limited field trials of 30,000 Km with LNG fuelled busses have been completed. It has been observed that LNG shows reduction of CO, THC and CH4 emissions and NOx emissions increased as compared to CNG. However, these values meet the BS VI emission norms. Oil sampling and analysis were undertaken after completion of every 100 hrs along with performance of the engine i.e. Power (kW), Torque (Nm) and brake specific fuel consumption (BSFC) (g/kWh) and emission characteristics. Engine performance was found satisfactory during endurance test. Developed engine oil demonstrated excellent behavior with LNG fuel and used engine oil physicochemical properties i.e. Kinematic viscosity@100°C, Total Base number (TBN), Total acid number (TAN), oxidation, nitration and wear elements (Iron (Fe), Copper (Cu), Aluminum (AL), Lead (Pb)) were reported well within the permissible limit. The study shows that the lubricant can be used for LNG application.