EFFECT OF HYDROGEN ENRICHMENT ON COMBUSTION AND EMISSIONS OF A HEAVY DUTY NATURAL GAS - DIESEL DUAL FUEL ENGINE AT LOW AND MEDIUM LOAD CONDITIONS

Diesel engines are widely used due to their higher reliability and superior fuel conversion efficiency. However, they generate significant amount of carbon dioxide (CO2) and particulate matter (PM) emissions. Natural gas is a low carbon and clean fuel that generates less CO2 and PM emissions than diesel during combustion. Replacing diesel by natural gas in internal combustion engines helps reduce both CO2 and PM emissions. A practical and efficient way to replace diesel by natural gas is natural gas - diesel dual fuel combustion. One concern for natural gas - diesel dual fuel combustion engines is the methane slip which offsets the advantage of low CO2 and PM emissions of natural gas combustion. Hydrogen enrichment enhances the burning rates and extends flammability limits of hydrocarbon fuels, and therefore has potential to help address the issue of methane slip in natural gas - diesel dual fuel engines. This paper investigated the effect of hydrogen enrichment on combustion and emissions of a heavy duty natural gas - diesel dual fuel engine at low and medium load conditions. About 45% volume based hydrogen was blended with natural gas and introduced into the cylinder via engine intake manifold of a single cylinder heavy duty research engine. Overall 75% diesel was displaced by hydrogen enriched natural gas. The results revealed that hydrogen enrichment reduced methane emissions by about 44 to 58% at the investigated conditions. Meanwhile, hydrogen enrichment also improved engine efficiency at most operation conditions, especially when methane slip was significant. As a result, hydrogen enrichment helped reduce CO2 equivalent emissions by about 17 to 38% compared to natural gas only - diesel dual fuel operation, although the overall energy fraction from hydrogen in the fuel input to the cylinder was less than 15%. Hydrogen enrichment also significantly decreased carbon monoxide emissions. A side effect of hydrogen enrichment was the increase in NOx emissions.