TY - JOUR

T1 - Experimental and numerical investigations of charge motion and combustion in lean-burn natural gas engines

AU - Korb, Benjamin

AU - Kuppa, Kalyan

AU - Nguyen, Hoang Dung

AU - Dinkelacker, Friedrich

AU - Wachtmeister, Georg

N1 - Funding information: The authors thank the Forschungsvereinigung Verbrennungskraftmaschinen (FVV) and the Fachagentur Nachwachsende Rohstoffe (FNR) as well as the Federal Ministry of Food and Agriculture (BMEL) for the financial support (FVV- Project-No. 1127 / FNR- FKZ 22407512 and 22407612 ).

PY - 2020/2

Y1 - 2020/2

N2 - It is important to understand the lean-burn combustion process of large-bore natural gas engines and influences on it in order to improve next generations of gas engines to meet the increasing requirements for high efficiencies and low emissions. The investigations in this study focus on the ignition and early flame propagation phase using optical experiments on a single-cylinder research engine, since both phases highly influence the subsequent main-combustion. Scavenged prechambers with different operating conditions and a tangential and radial nozzle alignment as well as unscavenged prechamber and direct spark plug ignition are compared. Beside the phenomenology of the ignition system itself, the interaction of the main-chamber charge motion and the ignition system is important to understand. Therefore, different valve timings (conventional timings and Miller cycle) as well as a low and high turbulence setup are subject of the study. Numerical simulations of the cold flow are used to understand the charge motion and mixture formation in the prechamber as well as in the main-chamber. The experiments depict an enhancement of the first flame propagation phase using a scavenged prechamber due to hot turbulent jets emerging from the nozzles. Furthermore, an influence of the nozzle geometry and the boundary conditions on the jet development and on the early flame propagation is observed. It is seen by the optical measurements that cycle-to-cycle variations can originate from the hot turbulent jets and its influence on the ignition of the main-chamber charge. Further, the optical measurements show that a low in-cylinder swirl and turbulence due to Miller cycle has an impact on the interaction between the in-cylinder charge motion and the jets. A comparison between high turbulence and low turbulence in-cylinder flows on the combustion is carried out. It is shown that the scavenged prechamber can compensate the lack of turbulence in the main-chamber. Hence, the scavenged prechamber enhances the flame propagation due to induced turbulence in the main-chamber and larger flame front surfaces generated by penetrating flame torches.

AB - It is important to understand the lean-burn combustion process of large-bore natural gas engines and influences on it in order to improve next generations of gas engines to meet the increasing requirements for high efficiencies and low emissions. The investigations in this study focus on the ignition and early flame propagation phase using optical experiments on a single-cylinder research engine, since both phases highly influence the subsequent main-combustion. Scavenged prechambers with different operating conditions and a tangential and radial nozzle alignment as well as unscavenged prechamber and direct spark plug ignition are compared. Beside the phenomenology of the ignition system itself, the interaction of the main-chamber charge motion and the ignition system is important to understand. Therefore, different valve timings (conventional timings and Miller cycle) as well as a low and high turbulence setup are subject of the study. Numerical simulations of the cold flow are used to understand the charge motion and mixture formation in the prechamber as well as in the main-chamber. The experiments depict an enhancement of the first flame propagation phase using a scavenged prechamber due to hot turbulent jets emerging from the nozzles. Furthermore, an influence of the nozzle geometry and the boundary conditions on the jet development and on the early flame propagation is observed. It is seen by the optical measurements that cycle-to-cycle variations can originate from the hot turbulent jets and its influence on the ignition of the main-chamber charge. Further, the optical measurements show that a low in-cylinder swirl and turbulence due to Miller cycle has an impact on the interaction between the in-cylinder charge motion and the jets. A comparison between high turbulence and low turbulence in-cylinder flows on the combustion is carried out. It is shown that the scavenged prechamber can compensate the lack of turbulence in the main-chamber. Hence, the scavenged prechamber enhances the flame propagation due to induced turbulence in the main-chamber and larger flame front surfaces generated by penetrating flame torches.

KW - Combustion visualization

KW - Lean-burn

KW - Miller cycle

KW - Natural gas engine

KW - Turbulent jet ignition

UR - http://www.scopus.com/inward/record.url?scp=85075498476&partnerID=8YFLogxK

U2 - 10.1016/j.combustflame.2019.11.005

DO - 10.1016/j.combustflame.2019.11.005

M3 - Article

AN - SCOPUS:85075498476

VL - 212

SP - 309

EP - 322

JO - Combustion and Flame

JF - Combustion and Flame

SN - 0010-2180

ER -