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2 Combustion Engines

2 2019

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Experimental comparison of efficiency and emission levels of four-cylinder lean-burn passenger car-sized CNG engines with different ignition concepts

Soltic Patric, Hilfiker Thomas, Hutter Richard, Hänggi Severin

Combustion Engines

2019

R. 58, nr 1

27--35

Today’s passenger car CNG engines are based on petrol engines which typically have restrictions preventing the exploitation of the full potential of methane based fuels, especially if they have to be operated also on petrol as a second fuel. Additionally, the use of threeway-catalysis limits the engine operation to λ = 1. Here, we present the efficiency potential and the raw emission characteristics for a dedicated four cylinder passenger car CNG engine without sticking to the usual combustion peak pressure and λ limitations. Lean combustion reduces the knocking tendency but, because of the higher pressure levels, increases the ignition energy demand. Therefore, different ignition systems (spark plug, prechamber, Diesel pilot) have been used.

Control-oriented analysis of a lean-burn light-duty natural gas research engine with scavenged pre-chamber ignition

Hänggi Severin, Hilfiker Thomas, Soltic Patric, Hutter Richard, Onder Christopher

Combustion Engines

2019

R. 58, nr 1

42--53

Natural gas is well-suited as a fuel in the transport sector. Due to its excellent combustion characteristics, engines operating with compressed natural gas (CNG) reach high efficiency, especially if operated at lean conditions. However, CNG engine research mainly focusses on stoichiometric conditions in order to use a three-way catalytic converter for the exhaust gas after treatment system. With the objective to explore the potential of CNG engines operated at lean conditions, a turbo-charged CNG engine with high compression ratio is developed and optimized for lean operation. In order to increase the ignition energy, the CNG engine is equipped with scavenged pre-chambers. A specific control structure is developed, which allows to operate the engine at a pre-defined (lean) air-to-fuel ratio. Further functionalities such as the combustion placement control and algorithms to estimate the conditions inside of the prechamber are implemented. The first part of this paper describes this engine control structure, which is specifically developed for the lean-burn CNG engine. In the second part, the effects of pre-chamber scavenging on engine performance criteria such as the combustion stability, engine efficiency or engine emissions are analyzed. With the objective to use pre-chamber scavenging to improve engine performance, a scavenging feedback control strategy is proposed. In order to control the ignition delay, this strategy adapts the amount of CNG injected into the prechamber with a linear controller or an extremum seeking algorithm depending on the air-to-fuel ratio of the main chamber.