• Transactions of the Korean Society of Automotive Engineers
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• v.21 no.2
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• pp.146-153
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• 2013

CNG buses has contributed to improve air quality in cities. But it is difficult to meet the next emission regulations such as EURO-VI without the help of additional post-processing device. Hydorgen has higher flame speed and lower combustion temperature that make it thermal efficiency increase with leaner operation. Using hydrogen natural gas blend (HCNG) fuel is promising technology which can reduce $NO_x$ and $CO_2$ emissions for a natural gas vehicle. However, fuel flow rate of HCNG should be increased since hydrogen's energy density per volume is much smaller than natural gas. In the present study, the characteristics of fuel supply system and its applicability were evaluated in a heavy duty natural gas engine. The results showed that the potential of fuel pressure regulator and fuel metering valve had enough capacity with HCNG. Employed mixer did not affect the distribution characteristics of mixture.

• Journal of the Korean Institute of Gas
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• v.20 no.6
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• pp.23-30
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• 2016

The conventional natural gas engine realized lean combustion for the improved efficiency. However, in order to cope with exhaust gas regulations enforced gradually, the interest has shifted at the stoichiometric mixture combustion system. The stoichiometric mixture combustion method has the advantage of a three-way catalyst utilization whose purification efficiency is high, but the problem of thermal durability and the fuel economy remains as a challenge. Hydrogen-natural gas blend fuel (HCNG) can increase the rate of exhaust gas recirculation (EGR) because the hydrogen increases burning speed and lean flammability limit. The increase in the EGR rate can have a positive impact on heat resistance of the engine due to the decreased combustion temperature, and further can increase the compression ratio for efficient combustion. In this study, to minimize the exhaust emission developed HCNG engine with stoichiometric combustion method, developed three-way catalyst was applied to evaluate the conversion characteristics. The tests were carried out during the steady state and transient operating conditions, and the results were compared for both the conventional and proto-three-way catalyst of HCNG engine for city buses.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.5
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• pp.473-479
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• 2013

This study focused on a heavy-duty natural gas engine fuelled with HCNG (CNG: 70 vol%, hydrogen: 30 vol%) and CNG. To study the emission characteristics of an HCNG engine with high compression ratio, the exhaust gas of CNG and HCNG fuel were analyzed in relation to the change in the compression ratio at the half load condition. The results showed that the thermal efficiency improved with an increase in the compression ratio. Consequently, $CO_2$ emission decreased. CO emission increased with inefficient oxidation due to the low exhaust gas temperature. $NO_x$ emission with high compression ratio was increased at the same excess air ratio condition. However, $NO_x$ emission was not affected by a compression ratio exceeding ${\lambda}$ = 1.9 because of the same MBT timing.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.4
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• pp.387-394
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• 2013

Hydrogen-compressed natural gas (HCNG) blend has attracted attention as a fuel that can reduce $CO_2$ emissions because it has low carbon content and burns efficiently. An increase in the compression ratio of HCNG engines was considered as one of the methods to improve their efficiency and reduce $CO_2$ emissions. However, a high combustion rate and flame temperature cause abnormal combustion such as pre-ignition or knocks, which in turn can cause damage to the engine components and decrease the engine power. In this study, the performance and knock characteristics with a change in the compression ratio of an HCNG engine were analyzed. The combustion characteristics of HCNG fuel were evaluated as a function of the excess air ratio using a conventional CNG engine. The effects of the compression ratio on the engine performance were evaluated through the same experimental procedures.