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Reduction of carbon dioxide (CO₂) emission, which causes global warming, is an important guideline for vehicle engine development. There are two types of methods for reducing the CO₂ emission of a vehicle engine. The first involves improving engine efficiency. The second involves the use of a low-carbon fuel, i.e., fuel with high hydrogen to carbon ratio. Hydrogen-compressed natural gas blend (HCNG) has been researched as a low-carbon fuel. Given that thermal efficiency of an engine cycle increases with its compression ratio (CR), an HCNG engine with high compression ratio not only has high efficiency but also low CO₂ emission. However, unexpected combustion such as knock could occur owing to the increased CR. In this study, we investigated the knock and emission characteristics of an 11-L heavy-duty HCNG engine with a modified CR. A conventional CNG engine was fuelled with HCNG30 (CNG 70 vol% and hydrogen 30 vol%).

Efforts have been made to apply biogas to an IC engine for power generation as a way to cope with the energy crisis as well as to reduce greenhouse gas. However, due to its gas component variations by origin and low energy density, using biogas in the engine applications and achieving a steady power generation is not an easy task. One way to overcome these deficiencies is to add hydrogen in biogas. Because of the excellent combustion characteristics of hydrogen, use of hydrogen-biogas blend fuel can allow not only accomplishing stable in-cylinder combustion, but also reducing the harmful emissions such as THC and CO. Despite several advantages of this approach, there exists a major drawback~a significant increase in NOx emission caused by high adiabatic combustion temperature of hydrogen.

This paper has investigated the effects of High Pressure Loop (HPL) and Low Pressure Loop (LPL) Exhaust Gas Recirculation (EGR) gas mixture on combustion and emissions characteristics in a light-duty automotive diesel engine. This mixed supply strategy of dual-loop EGR is expected to be efficient for the reduction of NOxand smoke without the loss of turbocharger power. The results from the combined HPL and LPL EGR system were compared with those from only HPL EGR and only LPL EGR system respectively. Characteristics including temperature and mass flow rates of intake charge, air excess ratio, O₂ concentration in intake charge, difference in pressure between intake and exhaust, pumping loss, fuel consumption, CO, HC, NOx emissions, and smoke opacity were compared and analyzed at two operating conditions. Fuel consumption, NOx emission, and smoke were reduced with dual EGR mixture.