Olsson, Jan-Ola, Tunestål, Per, Ulfvik, Jonas, and Johansson, Bengt
SAE 2003 World Congress and Exhibition,Detroit, Michigan, United States,-- SAE Special Publications. 2003(1742):21-38
EGR, Combustion, HCCI, Engine, Teknik, Maskinteknik, Energiteknik, Engineering and Technology, Mechanical Engineering, and Energy Engineering
This paper discusses the effects of cooled EGR on a turbocharged multi-cylinder HCCI engine. A six-cylinder, 12-liter, Scania D12 truck engine is modified for HCCI operation. It is fitted with port fuel injection of ethanol and n-heptane and cylinder pressure sensors for closed-loop combustion control. The effects of EGR are studied in different operating regimes of the engine. During idle, low speed and no load, the focus is on the effects on combustion efficiency, emissions of unburned hydrocarbons and CO. At intermediate load, run without turbocharging to achieve a well-defined experiment, combustion efficiency and emissions from incomplete combustion are still of interest. However the effect on NOdx and the thermodynamic effect on thermal efficiency, from a different gas composition, are studied as well. At high load and boost pressure the main focus is NOdx emissions and the ability to run high mean effective pressure without exceeding the physical constraints of the engine. In this case the effects of EGR on boost and combustion duration and phasing are of primary interest. It is shown that CO, HC and NOdx emissions in most cases all improve with EGR compared to lean burn. Combustion efficiency, which is computed based on exhaust gas analysis, increases with EGR due to lower emissions of CO and HC.
Einewall, Patrik, Tunestål, Per, and Johansson, Bengt
SAE 2003 World Congress and Exhibition,Detroit, Michigan, United States,-- SAE Special Publications. 2003(1749)
Spark Ignition, Control, CNG, Natural Gas, Ion Current, Teknik, Maskinteknik, Energiteknik, Engineering and Technology, Mechanical Engineering, and Energy Engineering
Ion current measurements can give information useful for controlling the combustion stability in a multi-cylinder engine. Operation near the dilution limit (air or EGR) can be achieved and it can be optimized individually for the cylinders, resulting in a system with better engine stability for highly diluted mixtures. This method will also compensate for engine wear, e.g., changes in volumetric efficiency and fuel injector characteristics. Especially in a port-injected engine, changes in fuel injector characteristics can lead to increased emissions and deteriorated engine performance when operating with a closed-loop lambda control system. One problem using the ion-current signal to control engine stability near the lean limit is the weak signal resulting in low signal-to-noise ratio. Measurements presented in this paper were made on a turbocharged 9.6-liter, six-cylinder natural gas engine with port injection. Each cylinder was individually controlled by a cylinder control module (CCM). A high turbulence combustion chamber was used to be able to operate with highly diluted mixtures. Comparisons between lean and EGR (stoichiometric) operation were made to investigate the potential of using the ion-current signal to control engine stability (cylinder-to-cylinder and cycle-to-cycle variations). A much stronger ion-current signal was found with EGR compared to lean operation, for the same load and comparable emissions.