• Transactions of the Korean hydrogen and new energy society
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• v.24 no.2
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• pp.136-141
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• 2013

In order to achieve simultaneously the ultra-low NOx, the high power and the high efficiency in a hydrogen-fueled engine with SI and the external mixture, the effects of low temperature combustion, performance and exhaust are compared and analyzed by the application of the lean boosting. As the results, the decrease rate of the high temperature in the hydrogen is less decreased than the other fuels by high constant-volume specific heat. However, when the conditions of 1.7bar and ${\Phi}=0.33$ are reached by the lean boosting, the maximum gas temperature of hydrogen is decreased under the temperature of NOx formation and it is possible to stabilize combustion below 2% of COVimep. Also, at that condition, it is feasible to achieve simultaneously NOx-free and the power of gasoline level. Therefore, it is found that the lean boosting is useful in the hydrogen-fueled engine.

• Transactions of the Korean hydrogen and new energy society
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• v.24 no.6
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• pp.573-579
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• 2013

Hydrogen engine with homogeneous charged compression ignition can achieve high efficiency by high compression ratio and rapid chemical reaction rates spatially. However, it needs to expansion of the operation range with over-all load conditions which is very narrow due to extremely high pressure rise rate. The adoption of the lean boosting in a HCCI $H_2$ engine is expected to be effective in expansion of operation range since minimum compression ratio for spontaneous ignition is decreased by low temperature combustion and increased surround in-cylinder pressure. In order to grasp its possibility by using lean boosting in the HCCI $H_2$ engine, compression ratio required for spontaneous ignition, expansion degree of the operation range and over-all engine performance are experimentally analyzed with the boosting pressure and supply energy. As the results, it is found that minimum compression ratio for spontaneous ignition is down to the compression ratio(${\varepsilon}$=19) of conventional diesel engine due to decreased self-ignition temperature, and operation range is extended to 170% in term of the equivalence ratio and 12 times in term of the supply energy than that of naturally aspirated type. Though indicated thermal efficiency is decreased by reduced compression ratio, it is over at least 46%.

• Journal of ILASS-Korea
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• v.26 no.4
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• pp.204-211
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• 2021

Lean combustion performance of natural gas and hydrogen was compared in a spark-ignition engine. The lean combustion engine operation with natural gas was limited due to combustion instability at an excess air ratio (EAR) above 1.8. The total hydrocarbon (THC) emissions increased significantly with increasing EAR. The nitrogen oxides (NO_X) emissions were also high due to the limitation of increasing EAR. The lean combustion engine operation with hydrogen showed superior combustion stability as well as low THC and NO_X emissions, even at high EARs. However, boosting technology was required to reach the high EARs.

• Journal of the Korean Institute of Gas
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• v.17 no.5
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• pp.8-14
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• 2013

Hydrogen-natural gas blends(HCNG) engine is optimizing technology of performance and emission characteristics with use of hydrogen's fast flame speed and wide flammability limit. As lean-burn limit is extended, the improvement in thermal efficiency and harmful emissions can be achieved. However, the extension of lean-burn limit under a wide open throttle operation point could be realized with the increase in boosting capacity in a lean-burn engine with turbo-charging system. In the present study, the power output characteristics of HCNG engine with turbo-charger change is assessed and feasibility of the increase in boosting capacity is evaluated. The turbo-charger design with high efficiency at higher flow rate rather than higher boosting pressure makes efficient operation possible at relatively rich mixture condition.

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.4
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• pp.455-462
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• 2006

Natural gas is a promising alternative fuel to meet strict engine emission regulations in many countries. Natural gas engines can operate at lean burn and stoichiometric burn conditions with different combustion and emission characteristics. In this paper, the fuel economy, emissions, misfire, knock and cycle-to-cycle variations in indicated mean effective pressure of lean burn natural gas engines are highlighted. Stoichiometric burn natural gas engines are briefly reviewed. To keep the output power and torque of natural gas engines comparable to that of gasoline engines, high boosting pressure should be used. High activity catalyst for methane oxidation and lean deNOx system or three way catalyst with precisely control strategies should be developed to meet stringent emission standards.

• Korean Journal of Construction Engineering and Management
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• v.20 no.6
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• pp.11-22
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• 2019

Current construction project processes pose difficulties for construction management as inefficient communication between project participants seldom accurately reflects the needs of the owner. To solve this problem, lean construction-based Integrated Project Delivery (IPD), which facilitates cooperation and builds trust through the formation of horizontal relationships among participants, is becoming increasingly popular. However, although lean construction-based IPD improves productivity in the construction industry, few studies have focused specifically on developing effective methods that maximize the benefits gained from lean construction-based IPD. This study therefore analyzed success factors for lean construction-based IPD projects by analyzing prior studies to identify factors that support IPD success. Application methods were analyzed and an example of how they are actually used in the field was examined through an in-depth single case analysis. The findings of this research can be applied to support lean construction-based IPD projects in Korea, improving their efficiency and boosting owner satisfaction.

• Journal of the Korean Institute of Gas
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• v.24 no.6
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• pp.1-10
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• 2020

Reactivity controlled compression ignition (RCCI) combustion is one of dual-fuel combustion systems which can be constructed by early diesel injection during the compression stroke to improve premixing between diesel and air. As a result, RCCI combustion promises low nitrogen oxides (NOx) and smoke emissions comparing to those of general dual-fuel combustion. For this combustion system, to meet the intensified emission regulations without emission after-treatment systems, exhaust gas recirculation (EGR) is necessary to reduce combustion temperature with lean premixed mixture condition. However, since EGR is supplied from the front of turbocharger system, intake pressure and the amount of fresh air supplementation are decreased as increasing EGR rate. For this reason, the effect of various EGR rates on the brake power and thermal efficiency of natural gas/diesel RCCI combustion under two different operating conditions in a 6 L compression ignition engine. Varying EGR rate would influence on the combustion characteristic and boosting condition simultaneously. For the 1,200/29 kW and 1,800 rpm/(lower than) 90 kW conditions, NOx and smoke emissions were controlled lower than the emission regulation of 'Tier-4 final' and the maximum in-cylinder pressure was 160 bar for the indurance of engine system. The results showed that under 1,200 rpm/29 kW condition, there were no changes in brake power and thermal efficiency. On the other hand, under 1,800 rpm condition, brake power and thermal efficieny were decreased from 90 to 65 kW and from 37 to 33 % respectively, because of deceasing intake pressure (from 2.3 to 1.8 bar). Therefore, it is better to supply EGR from the rear of compressor, i.e. low pressure EGR (LP-EGR) system, comparing to high pressure EGR (HP-EGR) for the improvement of RCCI power and thermal efficiency.