Investigation of the prechamber geometrical configuration of a natural gas spark ignition engine for cogeneration; part. II, experimentation

Daniel Favrat, Roger Röthlisberger
2003
Journal paper

Abstract

The operation of the small size cogeneration gas engine (6 cylinders, 122mm bore, 142mm stroke) modified for unscavenged prechamber ignition was experimentally investigated. The objective was to evaluate the potential to reduce the exhaust gas emissions, particulary the CO emissions, below the Swiss limits (NOx and CO emissions: 250 and 650 mg/m3N, 5 % O2, respectively), without exhaust gas after treatment, through variations of the prechamber geometrical configuration (size, number, distribution and orientation of the nozzle orifices and prechamber internal volume and shape). The results indicate that trends which increase the penetration of the gas jets and/or promote an early arrival of the flame front at the piston top land crevice entrance (small total nozzle orifice cross sectional area, limited number of nozzle orifices, an orientation of the nozzle orifices towards the squish region, relatively large prechamber internal volume) are benificial to reduce the CO and THC emissions. Further, these trends mainly result in a slight increase in fuel conversion efficiency.

Official source

https://infoscience.epfl.ch/record/53461?ln=en

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Related publications

The operation of a cogeneration internal combustion engine with unscavenged prechamber ignition was investigated. The objective was to evaluate the potential to reduce the exhaust gas emissions, particularly the CO emissions, without exhaust gas after treatment. The investigation was carried out on a small size gas engine (150kW) and required the development of cooled prechambers and the modification of the engine cylinder heads. The limit of the conventional lean burn operating mode with direct ignition is discussed and the prechamber geometrical configuration is presented. Through the generation of gas jets in the main chamber, the use of a prechamber strongly intensifies and accelerates the combustion process. The prechamber operation reduces significantly the emissions of CO and THC for same NOx emissions. The use of a piston generating significantly more turbulence leads to a somewhat higher fuel conversion efficiency without affecting significantly the CO and THC emissions at low NOx emissions. Further improvement associated with the adjustment of the engine operating parameters and the turbocharger characteristics, as well as a comparison between direct and prechamber ignition operation are presented in the second part (II) of this publication.

2001

In a first paper (part I), prechamber ignition in cogeneration natural gas engines has been shown to significantly intensify and accelerate the combustion process, offering a further potential to reduce the exhaust gas emissions while keeping efficiency at a high level. This second part discusses the influence of the engine operating parameters (spark timing and load) and the turbocharger characteristics with the objective of evaluating the potential to reduce the exhaust gas emissions, particularity the CO emissions, below the Swiss limits (NOx and CO emissions: 250 and 650 mg/m3N, 5% O2, respectively), without exhaust gas after treatment. The advantage of using an unscavenged prechamber is conditioned by a significant delay of the spark timing in order to generate substantial gas jets. This results in a large decrease in peak cylinder pressure and in an important reduction of NOx, CO and THC emissions. Minimum emissions are achieved at a spark timing of about 8°CABTDC . In comparison with the direct ignition, the prechamber ignition yields approximately 40% and 55% less CO and THC emissions, respectively. However, this also leads to about 2%-point lower fuel conversion efficiency. The optimisation of the turbocharger results in a recovery of about 1%-point in fuel conversion efficiency, but a consequent change in the exhaust manifold gas dynamics attenuates the reduction in THC emissions. At the rated power output (150kW), the prechamber ignition operation fulfils the Swiss requirements for exhaust gas emissions and still achieves a fuel conversion efficiency higher than 36.5%.

2002

An experimental investigation of a lean burn natural gas prechamber spark ignition engine for cogeneration

Roger Röthlisberger

The operation of a cogeneration internal combustion engine with unscavenged prechamber ignition was investigated. The objective was to evaluate the potential to reduce the exhaust gas emissions, particularly the CO emissions, below the Swiss limits (NOx and CO emissions: 250 and 650 mg/m3N, 5% O2 , respectively), without exhaust gas after treatment. The investigation was carried out on a small size gas engine (6 cylinders, 122 mm bore, 142 mm stroke) and required the development of cooled prechambers and the modification of the engine cylinder heads. The approach was essentially experimental, but included a numerical simulation based on the CFD-code KIVA-3V in order to assist and guide the experimentation. The numerical simulation was carried out in order to evaluate the differences in flow characteristics at the location of the spark plug electrodes between direct and prechamber ignition. Further, the influence of the prechamber geometrical configuration was investigated through variations of the nozzle orifice diameter, number and orientation, as well as prechamber volume and internal shape. Based on the results of the numerical simulation, the most promising prechamber configuration parameters were selected for experimentation. Then, variations of the selected prechamber configuration parameters, as well as of the piston geometry, of the turbocharger characteristics and of the engine operating parameters, were carried out in order to determine their influence on the engine performance and emissions. Through the generation of gas jets in the main chamber, the use of a prechamber strongly intensifies and accelerates the combustion process. However, this advantage is conditioned by a significant delay of the spark timing in order to generate substantial gas jets. This results in a large decrease in peak cylinder pressure and in an important reduction of NOx, CO and THC emissions. Minimum emissions are achieved at a spark timing of about 8°CABTDC. The prechamber geometrical parametric study indicates that trends which increase the penetration of the gas jets and/or promote an early arrival of the flame front at the piston top land crevice entrance are beneficial to reduce the CO and THC emissions. In comparison with the direct ignition, the prechamber ignition yields approximately 40% and 55% less CO and THC emissions, respectively. However, this also leads to about 2%-point lower fuel conversion efficiency. The optimisation of the turbocharger results in a recovery of about 1%-point in fuel conversion efficiency, but a consequent change in the exhaust manifold gas dynamics causes an increase in THC emissions. At the rated power output (150 kW), the prechamber ignition operation fulfils the Swiss requirements for exhaust gas emissions and still achieves a fuel conversion efficiency higher than 36.5%.

EPFL2001

An experimental investigation of a lean burn natural gas prechamber spark ignition engine for cogeneration

Roger Röthlisberger

The operation of a cogeneration internal combustion engine with unscavenged prechamber ignition was investigated. The objective was to evaluate the potential to reduce the exhaust gas emissions, particularly the CO emissions, below the Swiss limits (NOx and CO emissions: 250 and 650 mg/m3N, 5% O2 , respectively), without exhaust gas after treatment. The investigation was carried out on a small size gas engine (6 cylinders, 122 mm bore, 142 mm stroke) and required the development of cooled prechambers and the modification of the engine cylinder heads. The approach was essentially experimental, but included a numerical simulation based on the CFD-code KIVA-3V in order to assist and guide the experimentation. The numerical simulation was carried out in order to evaluate the differences in flow characteristics at the location of the spark plug electrodes between direct and prechamber ignition. Further, the influence of the prechamber geometrical configuration was investigated through variations of the nozzle orifice diameter, number and orientation, as well as prechamber volume and internal shape. Based on the results of the numerical simulation, the most promising prechamber configuration parameters were selected for experimentation. Then, variations of the selected prechamber configuration parameters, as well as of the piston geometry, of the turbocharger characteristics and of the engine operating parameters, were carried out in order to determine their influence on the engine performance and emissions. Through the generation of gas jets in the main chamber, the use of a prechamber strongly intensifies and accelerates the combustion process. However, this advantage is conditioned by a significant delay of the spark timing in order to generate substantial gas jets. This results in a large decrease in peak cylinder pressure and in an important reduction of NOx, CO and THC emissions. Minimum emissions are achieved at a spark timing of about 8°CABTDC. The prechamber geometrical parametric study indicates that trends which increase the penetration of the gas jets and/or promote an early arrival of the flame front at the piston top land crevice entrance are beneficial to reduce the CO and THC emissions. In comparison with the direct ignition, the prechamber ignition yields approximately 40% and 55% less CO and THC emissions, respectively. However, this also leads to about 2%-point lower fuel conversion efficiency. The optimisation of the turbocharger results in a recovery of about 1%-point in fuel conversion efficiency, but a consequent change in the exhaust manifold gas dynamics causes an increase in THC emissions. At the rated power output (150 kW), the prechamber ignition operation fulfils the Swiss requirements for exhaust gas emissions and still achieves a fuel conversion efficiency higher than 36.5%.

EPFL2001