Bose, P. and Banerjee, R., "Performance and Emission Characteristic Evaluation of a Single-Cylinder Four-Stroke Diesel Engine Running on Hydrogen and Diesel in Dual Fuel Mode Under Different EGR Conditions," SAE Technical Paper 2009-28-0038, 2009, https://doi.org/10.4271/2009-28-0038.
Hydrogen-fuelled internal combustion engines with near zero emissions and efficiencies exceeding today's port-fuel-injected engines are a potential near term option and a bridge to hydrogen fuel cell vehicles where fuel cell undergoes developments to make it economically viable. Hydrogen with its inherent high flame velocity enables a more isochoric, thus thermodynamically more favorable combustion than conventional diesel engines which undergo a pressure and temperature rise spread over several degrees of crank travel. Hydrogen has an exceptionally wide flammability limits compared to conventional fuels enabling the engine to work with very lean mixtures, thus omitting the necessity of a throttle valve~this ideally suits a diesel engine operation. Its high autoignition temperature helps to realize the working cycles at higher compression ratios and consequent higher brake thermal efficiencies. The present work attempts to explore the performance and emission characteristics of an existing single-cylinder four-stroke compression ignition engine operated in dual fuel mode with hydrogen as an alternative fuel. The hydrogen was premixed with the incoming air and inducted during the duration of intake valve opening by an indigenously developed electro-mechanical means of solenoid actuation. In this experiment hydrogen flow rate was kept constant at 0.15 kg/hr. The present study revealed a persistent increase of the brake thermal efficiency over the entire range of operation under all cases of hydrogen enrichment with a maximum increase of 15.73% at 40% load. The BSFC decreased with all cases of hydrogen enrichment showing a significant decrease of 63.3% at 20% load. Smoke emissions displayed a decrease for all cases of hydrogen enrichment with a decrease of 64.28% and 61.5% at 20% and 40% load respectively for non EGR cases, HC emissions decreased for the entire range of operation for hydrogen enrichment with a substantial decrease of 80.0% at 20% load and a 57.6% decrease at 80% load. CO emissions reduced by 69.5% and 64.5% at 20% and 40% loading with a trend of decrease for all hydrogen enrichment operations. Hydrogen enrichment displayed a steady decrease of CO2 for all ranges of operation with a decrease of 71.05% and 40.05% at 20% and 80% loading. The ultra-lean combustion characteristics of hydrogen provide the perfect environment for NOx emissions which are compounded with the inherent tendency of diesel fuel combustion. It thus creates a challenge to solve the paradox of simultaneously reducing NOx emissions and reap the benefits of using hydrogen in the context of reduced typical pollutant emissions of diesel engines. In our present work the suitability of different EGR techniques, both qualitatively and quantitatively, were examined in reducing NOx concentrations. The NOx level decreased from 1211 ppm to 710 for hydrogen enrichment (0.15 kg/hr) at 80% of the rated load under 20% cooled EGR.