Development of an Ultra-Low Carbon Flex Dual-Fuel Ammonia Engine for Heavy-Duty Applications 2024-01-2368

The work examined the practicality of converting a modern production 6 cylinder 7.7 litre heavy-duty diesel engine for flex dual-fuel operation with ammonia as the main fuel. A small amount of diesel fuel (pilot) was used as an ignition source. Ammonia was injected into the intake ports during the intake stroke, while the original direct fuel injection equipment was retained and used for pilot diesel injection. A bespoke engine control unit was used to control the injection of both fuels and all other engine parameters. The aim was to provide a cost-effective retrofitting technology for existing heavy-duty engines, to enable eco-friendly operation with minimal carbon emissions. The tests were carried out at a baseline speed of 600 rpm for the load range of the engine (10-90%), with minimum pilot diesel quantity and as high as 90% substitution ratio of ammonia for diesel fuel. Results demonstrated that at high load conditions, ammonia dual-fuel operation could achieve diesel-like efficiency, while reducing engine carbon emissions by 90% and almost eliminating soot. Engine stability was maintained at acceptable levels, while the peak in-cylinder pressure and the maximum rate of pressure rise were reduced by more than 7% and 34%, respectively. Despite slightly lower combustion and exhaust gas temperatures, ammonia dual-fuel operation resulted in higher NOx emissions compared with conventional diesel operation, potentially owing to the nitrogen-rich fuel. The case was reversed at low load conditions, where ammonia dual-fuel operation produced lower NOx emissions but suffered poor combustion and inferior engine performance, relative to conventional diesel operation. Ammonia slip into the exhaust was excessive (exceeding 10,000 ppm) throughout dual-fuel testing.