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Low Load Operation on high Octane Gasoline PPC in a Light Duty Engine using Negative Valve Overlap and NVO-pilot injection

Marku, Olivian and Arvidson, Hjalmar (2012) In ISRN LUTMDN/TMHP--12/5248--SE
Department of Energy Sciences
Abstract
Although development of electrical vehicles seems to go forward, they are still best suitable for short range transportation, and are dependent of generation of clean electricity to be environmental friendly. The fuel cell has issues to be solved, for example low efficiency at loading, and also problem of generating and storing the hydrogen fuel in an efficient way. Recent years the hybrid vehicle has become popular, and it should be seen as a way to combine the best of the electrical vehicle with the combustion engine.
The combustion engine seems to remain as the main propulsion device for transportation for the near future, as it combines reliability with low cost, can use a variety of fuels, and the fuels are easy to distribute. The... (More)
Although development of electrical vehicles seems to go forward, they are still best suitable for short range transportation, and are dependent of generation of clean electricity to be environmental friendly. The fuel cell has issues to be solved, for example low efficiency at loading, and also problem of generating and storing the hydrogen fuel in an efficient way. Recent years the hybrid vehicle has become popular, and it should be seen as a way to combine the best of the electrical vehicle with the combustion engine.
The combustion engine seems to remain as the main propulsion device for transportation for the near future, as it combines reliability with low cost, can use a variety of fuels, and the fuels are easy to distribute. The diesel engine is popular for its lower fuel consumption and CO2 emissions than the gasoline powered spark ignition engine. The major drawback of the diesel engine is the emissions of smoke and nitric oxides, NOx.
As crude oil prices are rising and emissions legislations become more stringent, there has been interest for new combustion concepts. One of the most promising is Partially Premixed Combustion, PPC, which can combine the low emissions of a spark ignition engine with the high efficiency of the diesel engine.
Partially Premixed Combustion (PPC) is, like its close relative HCCI, a low temperature combustion technique that can result in improved efficiency and low emissions of particulate matter and NOx. By using gasoline, instead of diesel, higher loads and lower emissions is possible obtain.
While running gasoline PPC at high load has been investigated, the low load case has been more difficult to master. When the load is decreased less heat is produced, leading to ignitability problems. It is also assumed that the energy of the exhaust gases is not enough to generate the required boost at low load. If variable valve timing is used it is possible to use Negative Valve Overlap (NVO) to trap residual gases, and elevate the cylinder temperature and promote auto ignition, making lower load possible.
In this project a Volvo D5 passenger car diesel engine operated in single cylinder configuration was run in partially premixed combustion mode. Swedish diesel Mk1 and three gasoline fuels with different octane number were used. The engine was equipped with Cargine Engineering camless fully flexible valves.
The aim was to evaluate means to extend low load limitation with high octane gasoline. Different combinations of valve timing that resulted in different fractions of negative valve overlap were investigated, combined with fuel injection strategies and continually operated glow plug. Two different combustion chambers were also investigated.
III
The results show that negative valve overlap is a useful tool to obtain lower load operation in an engine operated in PPC with high octane gasoline.
As a complement to NVO, NVO-pilot injection was investigated, where the injected fuel is split into a main part and a part injected during the negative valve overlap. Different fractions of NVO-pilot were investigated. With NVO-pilot injection, combined with NVO, it was possible to reach lower loads. As the load is decreased, a higher portion of the fuel should be injected during the negative valve overlap.
The glow plug comparison showed that a continually operated glow has a small positive effect on low load operations running high octane gasoline PPC.
Finally, in the combustion chamber investigation it was found that a combustion chamber with a shallow bowl and deep valve pockets yielded in better results than the standard bowl shaped combustion chamber running PPC at low load.
With 69 RON gasoline 1 bar IMEPgross was easily reached, with no soot emissions and less EGR had to be used when compared with diesel to get the same NOx level.
With 87 RON gasoline lowest operating point with just one injection and NVO of 60 degrees was above 4 bar IMEPgross. Running with NVO and NVO-pilot injection, the lowest operating point was 1.2 bar IMEPgross.
With the same conditions using 97 RON gasoline, 2 bar IMEPgross was possible to reach with stable combustion, thus at the price of high level of HC and CO emissions. As a contrary to NOx, the HC and CO can be treated with a cost effective oxidizing catalyst. (Less)
Please use this url to cite or link to this publication:
author
Marku, Olivian and Arvidson, Hjalmar
supervisor
organization
year
type
H1 - Master's Degree (One Year)
subject
keywords
high octane gasoline light duty engine negative valve overlap NVO-pilot injection
publication/series
ISRN LUTMDN/TMHP--12/5248--SE
language
English
id
2541273
date added to LUP
2012-05-16 15:32:20
date last changed
2012-05-16 15:32:20
@misc{2541273,
  abstract     = {Although development of electrical vehicles seems to go forward, they are still best suitable for short range transportation, and are dependent of generation of clean electricity to be environmental friendly. The fuel cell has issues to be solved, for example low efficiency at loading, and also problem of generating and storing the hydrogen fuel in an efficient way. Recent years the hybrid vehicle has become popular, and it should be seen as a way to combine the best of the electrical vehicle with the combustion engine.
The combustion engine seems to remain as the main propulsion device for transportation for the near future, as it combines reliability with low cost, can use a variety of fuels, and the fuels are easy to distribute. The diesel engine is popular for its lower fuel consumption and CO2 emissions than the gasoline powered spark ignition engine. The major drawback of the diesel engine is the emissions of smoke and nitric oxides, NOx.
As crude oil prices are rising and emissions legislations become more stringent, there has been interest for new combustion concepts. One of the most promising is Partially Premixed Combustion, PPC, which can combine the low emissions of a spark ignition engine with the high efficiency of the diesel engine.
Partially Premixed Combustion (PPC) is, like its close relative HCCI, a low temperature combustion technique that can result in improved efficiency and low emissions of particulate matter and NOx. By using gasoline, instead of diesel, higher loads and lower emissions is possible obtain.
While running gasoline PPC at high load has been investigated, the low load case has been more difficult to master. When the load is decreased less heat is produced, leading to ignitability problems. It is also assumed that the energy of the exhaust gases is not enough to generate the required boost at low load. If variable valve timing is used it is possible to use Negative Valve Overlap (NVO) to trap residual gases, and elevate the cylinder temperature and promote auto ignition, making lower load possible.
In this project a Volvo D5 passenger car diesel engine operated in single cylinder configuration was run in partially premixed combustion mode. Swedish diesel Mk1 and three gasoline fuels with different octane number were used. The engine was equipped with Cargine Engineering camless fully flexible valves.
The aim was to evaluate means to extend low load limitation with high octane gasoline. Different combinations of valve timing that resulted in different fractions of negative valve overlap were investigated, combined with fuel injection strategies and continually operated glow plug. Two different combustion chambers were also investigated.
III
The results show that negative valve overlap is a useful tool to obtain lower load operation in an engine operated in PPC with high octane gasoline.
As a complement to NVO, NVO-pilot injection was investigated, where the injected fuel is split into a main part and a part injected during the negative valve overlap. Different fractions of NVO-pilot were investigated. With NVO-pilot injection, combined with NVO, it was possible to reach lower loads. As the load is decreased, a higher portion of the fuel should be injected during the negative valve overlap.
The glow plug comparison showed that a continually operated glow has a small positive effect on low load operations running high octane gasoline PPC.
Finally, in the combustion chamber investigation it was found that a combustion chamber with a shallow bowl and deep valve pockets yielded in better results than the standard bowl shaped combustion chamber running PPC at low load.
With 69 RON gasoline 1 bar IMEPgross was easily reached, with no soot emissions and less EGR had to be used when compared with diesel to get the same NOx level.
With 87 RON gasoline lowest operating point with just one injection and NVO of 60 degrees was above 4 bar IMEPgross. Running with NVO and NVO-pilot injection, the lowest operating point was 1.2 bar IMEPgross.
With the same conditions using 97 RON gasoline, 2 bar IMEPgross was possible to reach with stable combustion, thus at the price of high level of HC and CO emissions. As a contrary to NOx, the HC and CO can be treated with a cost effective oxidizing catalyst.},
  author       = {Marku, Olivian and Arvidson, Hjalmar},
  keyword      = {high octane gasoline light duty engine negative valve overlap NVO-pilot injection},
  language     = {eng},
  note         = {Student Paper},
  series       = {ISRN LUTMDN/TMHP--12/5248--SE},
  title        = {Low Load Operation on high Octane Gasoline PPC in a Light Duty Engine using Negative Valve Overlap and NVO-pilot injection},
  year         = {2012},
}