This study focuses NH3 as an alternative fuel for internal combustion engines, because NH3 is known as a H2 carrier and its combustion does not produce CO2 causing global warming. On the other hand, some reports show that unburned NH3 and N2O appear in exhaust gas, when NH3 is used as fuel for compression ignition or spark ignition engines. NH3 is toxic and N2O is one of the greenhouse gases. These emissions should not be emitted. These reports point out that exhaust gas after treatments and/or injection strategies can be effective to reduce these emissions. From our previous investigations, it was confirmed that NH3 and N2O were contained in the exhaust gas of a conventional diesel engine with NH3 gas mixed into the engine intake. In this study, NH3 combustion processes in the diesel engine were investigated from the experimental results. Based on the investigations, a pilot or postinjection was conducted to reduce emissions of NH3 and N2O. In this paper, first the experimental results of the combustion and exhaust emission characteristics on the conventional diesel engine with NH3 gas mixed into the engine intake are shown. NH3 and N2O emissions are then verified by analyzing the exhaust gas. Next, NH3 combustion processes in the diesel engine are considered from the experimental results to report on the effects of a pilot and postdiesel fuel injection on NH3 and N2O production processes. The experimental results suggest that the multiple diesel fuel injections would be one of the effective measures to reduce N2O and NH3 emissions on NH3 and diesel dual-fueled engine.

It is well known that ammonia (NH3) combustion does not produce carbon dioxide (CO2) causing global warming. Therefore, NH3 has received much attention as an alternative diesel fuel for internal combustion engines. On the other hand, it has been reported that the exhaust gas of diesel engine fumigated with NH3 contains unburned NH3 with toxicity for humans and nitrous oxide (N2O) with strong global warming effect. Hence the NH3 and N2O emissions should be reduced to prevent the human health damage and global warming. The aim of this study was to develop the combustion strategies for reducing the unburned NH3 and N2O emissions on diesel engine fumigated with NH3. The experimental results indicated that the higher temperature combustion of NH3 prevents the N2O production and allows itself to react well. From the numerical simulation results, hydrocarbon combustion decomposes NH3 and N2O in ignition processes.

The need for reductions of nitrogen oxides (NOx), sulfur oxides (SOx), and carbon dioxide (CO2) emissions has been acknowledged on the global level. However, it is difficult to meet the strengthened emissions regulations by using the conventional marine diesel engines. Therefore, lean burn gas engines have been recently attracting attention in the maritime industry. Because they use natural gas as fuel and can simultaneously reduce both NOx and CO2 emissions. On the other hand, since methane is the main component of natural gas, the slipped methane, which is the unburned methane emitted from the lean burn gas engines, might have a potential impact on global warming. The authors have proposed a combined exhaust gas recirculation (C-EGR) system to reduce the slipped methane from the gas engines and NOx from marine diesel engines by providing the exhaust gas from lean burn gas engine to the intake manifold of the marine diesel engine using a blower. Since the exhaust gas from the gas engine includes slipped methane, this system could reduce both the NOx from the marine diesel engine and the slipped methane from the lean burn gas engine simultaneously. This paper introduces the details of the proposed C-EGR system and presents the experimental results of emissions characteristics on the C-EGR system. As a result, it was confirmed that the C-EGR system attained more than 75% reduction of the slipped methane in the intake gas. Additionally, the NOx emission from the diesel engine decreased with the effect of the exhaust gas recirculation (EGR) system.

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Lean-burn gas engines have recently attracted attentions in the maritime industry, because they can reduce NOx, SOx and CO2 emissions. However, since CH4 is the main component of natural gas, the slipped methane which is the unburned methane emitted from the lean-burn gas engines likely contributes to global warming. It is thus important to make progress on exhaust aftertreatment technologies for lean-burn gas engines. Pd catalysts for CH4 oxidation is expected to provide a countermeasure for slipped methane, because it can activate at lower exhaust temperature. However, a deactivation in higher H2O concentration should be overcome, because H2O inhibits CH4 oxidation. This study was performed investigates the effects of exhaust temperature or gas composition on active Pd catalyst sites to clarify CH4 oxidation performance in the exhaust gas of lean-burn gas engines. The authors developed the method of estimating effective active sites for the Pd catalyst at various exhaust temperature. The estimation method is based on the assumption that active sites used for CH4 oxidation can be shared with that used for CO oxidation. To clarify the effects of exhaust temperature and compositions on active Pd catalyst sites, the authors developed an experimental system for the new estimation method. This paper introduces experimental results and verifications of the new method, showing that chemisorbed CO volume on a Pd/Al2O3 catalyst is increased with increasing Pd loading in 250–450 ºC, simulated as a typical exhaust temperature range of lean-burn gas engines.