A comparative study of lean burn and exhaust gas recirculation in an HCNG-fueled heavy-duty engine. (12th October 2017)

• Record Type: Journal Article
• Authors: Park, Cheolwoong; Lee, Sunyoup; Kim, Changgi; Choi, Young
• Is Part Of: International journal of hydrogen energy. Volume 42:Number 41(2017)
• Page Start: 26094
• Page End: 26101
• Publication Date: 2017-10-12
• Subjects: CNG -- HCNG -- Lean burn -- Exhaust gas recirculation -- Thermal efficiency -- Emissions; Hydrogen as fuel -- Periodicals; Hydrogène (Combustible) -- Périodiques; Hydrogen as fuel; Periodicals; 665.81
• DOI: 10.1016/j.ijhydene.2017.08.170
• Languages: English
• ISSNs: 0360-3199

Abstract

Abstract: Two dilution strategies, exhaust gas recirculation (EGR) with a stoichiometric mixture and excess air with a lean mixture, were investigated for an 11 L, 6-cylinder H2 -blended compressed natural gas (HCNG) engine. The engine was operated at 1260 rpm and 50% of maximum engine load (575 Nm) at maximum brake torque for each strategy. To evaluate the EGR approach, the stoichiometric combustion mode was varied, and to evaluate the lean combustion mode, the excess air ratio was varied. The maximum EGR rate and lean flammability limit were constrained by the combustion stability. The dilution rate was employed to compare the dilution effect on engine performance and emission levels under identical levels of the dilution for both combustion modes. The thermal efficiencies under stoichiometric combustion with EGR were lower than those under lean combustion, owing to a higher pumping loss and a lower combustion speed. The total hydrocarbon emissions under the lean combustion mode were lower than those under the stoichiometric combustion mode only when the combustion speed was relatively slow, due to the higher mixing rate caused by the active combustion. As the dilution rate was increased in the lean combustion mode, the rate of decrease in NOx emissions slowed compared to the stoichiometric combustion mode. The lowest level of engine-out NOx emissions was observed under lean combustion. Highlights: The maximum dilution rates of an HCNG engine are 27.3% for EGR and 48.6% for lean-burn. The efficiency with EGR is lower owing to pumping loss and combustion temperature. THC emissions with lean-burn are lower under a low combustion speed because of mixing rate. The lowest level of engine-out NOx is observed with lean-burn.