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Diluted Operation of a Heavy-Duty Natural-gas Engine

Kaiadi, Mehrzad LU (2008)
Abstract
Fuel economy and emissions are the two central parameters in heavy duty engines; most of the existing heavy duty engines are run with diesel. The overall efficiency of diesel engines is good however they suffer from high levels of emissions mainly NOX and soot. Using alternative fuels like Natural-Gas has shown to be a good way to reduce emissions level. Diesel engines can be easily converted to Natural-Gas engines which is a very cost effective way for producing Natural-Gas engines.



High EGR rates combined with turbocharging has been identified as a promising way to increase the maximum load and efficiency of heavy duty spark ignition Natural-Gas engines. With stoichiometric conditions a three way catalyst can be used... (More)
Fuel economy and emissions are the two central parameters in heavy duty engines; most of the existing heavy duty engines are run with diesel. The overall efficiency of diesel engines is good however they suffer from high levels of emissions mainly NOX and soot. Using alternative fuels like Natural-Gas has shown to be a good way to reduce emissions level. Diesel engines can be easily converted to Natural-Gas engines which is a very cost effective way for producing Natural-Gas engines.



High EGR rates combined with turbocharging has been identified as a promising way to increase the maximum load and efficiency of heavy duty spark ignition Natural-Gas engines. With stoichiometric conditions a three way catalyst can be used which means that regulated emissions can be kept at very low levels. However efficiencies of Natural-Gas engines are lower than the corresponding diesel versions due to throttling losses. These losses are higher at low/part loads. Using EGR at lower loads can increase the efficiency; however obtaining reliable spark ignition is difficult with high pressure and dilution. There is a limit to the amount of EGR that can be tolerated for each operating point. A combustion stability parameter should indicate the EGR tolerance of the engine.



Different combustion stability parameters derived from pressure and ion-current signals are applied in order to control the dilution limit with EGR. Furthermore closed-loop lambda control is applied to control air/fuel ratio. With help of these controllers and also a load controller, a tool is developed for finding the best positions of the throttle and EGR valve where the engine has its highest dilution while the engine stability is preserved. Two papers are written based on the results of this study i.e. in the first one the combustion stability is based on the pressure signals and in the second one the combustion stability is derived from ion-current signals. The proposed control strategy has been successfully tested on a heavy duty 6-cylinder port-injected natural-gas engine and the results show 1.5-2.5 % units improvement in Brake Efficiency.



In another experiment, behaviour of the engine was investigated by running the engine with Hythane (Natural gas + 10% Hydrogen ) when the engine operates stoichiometric. Data from running a lean burn natural-gas engine with Hythane was available and it was desired to see the behavior of the engine with stoichiometric operation. The results do not show significant changes in knock margins, efficiency and emissions with stoichiometric operation. However, Lean limit and dilution limit can be extended somewhat by Hythane. (Less)
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5381ce85-9c7f-4e07-95d1-f2fbdbb91845 (old id 1396304)
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@misc{5381ce85-9c7f-4e07-95d1-f2fbdbb91845,
  abstract     = {Fuel economy and emissions are the two central parameters in heavy duty engines; most of the existing heavy duty engines are run with diesel. The overall efficiency of diesel engines is good however they suffer from high levels of emissions mainly NOX and soot. Using alternative fuels like Natural-Gas has shown to be a good way to reduce emissions level. Diesel engines can be easily converted to Natural-Gas engines which is a very cost effective way for producing Natural-Gas engines. <br/><br>
<br/><br>
High EGR rates combined with turbocharging has been identified as a promising way to increase the maximum load and efficiency of heavy duty spark ignition Natural-Gas engines. With stoichiometric conditions a three way catalyst can be used which means that regulated emissions can be kept at very low levels. However efficiencies of Natural-Gas engines are lower than the corresponding diesel versions due to throttling losses. These losses are higher at low/part loads. Using EGR at lower loads can increase the efficiency; however obtaining reliable spark ignition is difficult with high pressure and dilution. There is a limit to the amount of EGR that can be tolerated for each operating point. A combustion stability parameter should indicate the EGR tolerance of the engine. <br/><br>
<br/><br>
Different combustion stability parameters derived from pressure and ion-current signals are applied in order to control the dilution limit with EGR. Furthermore closed-loop lambda control is applied to control air/fuel ratio. With help of these controllers and also a load controller, a tool is developed for finding the best positions of the throttle and EGR valve where the engine has its highest dilution while the engine stability is preserved. Two papers are written based on the results of this study i.e. in the first one the combustion stability is based on the pressure signals and in the second one the combustion stability is derived from ion-current signals. The proposed control strategy has been successfully tested on a heavy duty 6-cylinder port-injected natural-gas engine and the results show 1.5-2.5 % units improvement in Brake Efficiency. <br/><br>
 <br/><br>
In another experiment, behaviour of the engine was investigated by running the engine with Hythane (Natural gas + 10% Hydrogen ) when the engine operates stoichiometric. Data from running a lean burn natural-gas engine with Hythane was available and it was desired to see the behavior of the engine with stoichiometric operation. The results do not show significant changes in knock margins, efficiency and emissions with stoichiometric operation. However, Lean limit and dilution limit can be extended somewhat by Hythane.},
  author       = {Kaiadi, Mehrzad},
  language     = {eng},
  title        = {Diluted Operation of a Heavy-Duty Natural-gas Engine},
  year         = {2008},
}