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Studies of the Combustion Process with Simultaneous OH- and Formaldehyde-PLIF in a Direct-Injected HCCI engine

Collin, Robert LU ; Nygren, Jenny LU ; Richter, Mattias LU ; Hildingsson, Leif LU and Johansson, Bengt LU (2004) Sixth International Symposium on Diagnostics and Modeling of Combustion in Internal Combustion Engines In [Host publication title missing] p.311-317
Abstract
To run a Diesel engine in Homogeneous Charge Compression Ignition (HCCI) mode has proved to be a highly promising approach towards reduced engine-out emissions of NOx and particulate matter. A crucial issue when utilizing HCCI is the degree of charge homogeneity that is required to achieve the desired low temperature combustion. A very well mixed charge can be created through the use of traditional port injection. This approach would most often result in low emissions of NOx and soot. However, this strategy might also see a penalty in the form of high levels of unburned hydrocarbons due to incomplete combustion, especially under low load conditions. A proposed solution to this is to utilize stratified charge in the lower load range. The... (More)
To run a Diesel engine in Homogeneous Charge Compression Ignition (HCCI) mode has proved to be a highly promising approach towards reduced engine-out emissions of NOx and particulate matter. A crucial issue when utilizing HCCI is the degree of charge homogeneity that is required to achieve the desired low temperature combustion. A very well mixed charge can be created through the use of traditional port injection. This approach would most often result in low emissions of NOx and soot. However, this strategy might also see a penalty in the form of high levels of unburned hydrocarbons due to incomplete combustion, especially under low load conditions. A proposed solution to this is to utilize stratified charge in the lower load range. The creation of a stratified charge imposes no major problems in modern DI engines. The important parameter is the degree of stratification that can be tolerated. If the charge gets too highly stratified, the combustion will become more diesel-like with dramatically increased levels of NOx and soot as a result.

This paper presents simultaneous laser based measurements of formaldehyde and OH-radical distributions in an HCCI engine. Formaldehyde is formed as an intermediate species when combusting hydrocarbons. The formation occurs through low temperature reactions in an early phase of the combustion process. Later in the process formaldehyde is being consumed. Formaldehyde is, therefore, used as indicator of the first stage of combustion and a marker of zones with low-temperature reactions. The OH radical is formed as an intermediate during the high temperature reactions, and is used as a marker of zones where the combustion is ongoing. The purpose of the investigation was to study how the combustion process is affected by the change in homogeneity that arises from early and late injection, respectively.

A 0.5 liter single-cylinder optical engine equipped with a DI common rail fuel system was operated with a number of different injection timings, resulting in various levels of charge stratification. A blend of iso-octane and n-heptane was used as fuel. The measurement technique used was planar laser-induced fluorescence where formaldehyde was excited at 355nm and OH at 283nm. Two separate ICCD units were used to detect the resulting fluorescence from formaldehyde and OH. Measurement series covering the process from the start of injection until late in the expansion stroke is presented for different injection timings as well as pressure traces and emission analysis. A homogeneity index is calculated and used to compare the level of homogeneity resulting from injection timings. From early injection until about 50CAD BTDC the time, between onset of low temperature reactions and start of the high temperature reactions, is long enough for the formaldehyde to form an almost homogeneous distribution before it is being consumed. For later injection timings the high temperature reactions starts before this mixing is completed and therefore the formaldehyde distribution is not longer homogeneous and the combustion is more diesel like. (Less)
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author
organization
publishing date
type
Chapter in Book/Report/Conference proceeding
publication status
published
subject
keywords
HCCI, Direct-Injection, Formaldehyde, OH, PLIF
in
[Host publication title missing]
pages
7 pages
publisher
The Japan Society of Mechanical Engineers, JSME
conference name
Sixth International Symposium on Diagnostics and Modeling of Combustion in Internal Combustion Engines
language
English
LU publication?
yes
id
79b7ba95-4520-44d1-ad74-6ed6da80f0a9 (old id 4935843)
date added to LUP
2015-01-19 14:14:19
date last changed
2016-04-16 09:59:06
@misc{79b7ba95-4520-44d1-ad74-6ed6da80f0a9,
  abstract     = {To run a Diesel engine in Homogeneous Charge Compression Ignition (HCCI) mode has proved to be a highly promising approach towards reduced engine-out emissions of NOx and particulate matter. A crucial issue when utilizing HCCI is the degree of charge homogeneity that is required to achieve the desired low temperature combustion. A very well mixed charge can be created through the use of traditional port injection. This approach would most often result in low emissions of NOx and soot. However, this strategy might also see a penalty in the form of high levels of unburned hydrocarbons due to incomplete combustion, especially under low load conditions. A proposed solution to this is to utilize stratified charge in the lower load range. The creation of a stratified charge imposes no major problems in modern DI engines. The important parameter is the degree of stratification that can be tolerated. If the charge gets too highly stratified, the combustion will become more diesel-like with dramatically increased levels of NOx and soot as a result.<br/><br>
This paper presents simultaneous laser based measurements of formaldehyde and OH-radical distributions in an HCCI engine. Formaldehyde is formed as an intermediate species when combusting hydrocarbons. The formation occurs through low temperature reactions in an early phase of the combustion process. Later in the process formaldehyde is being consumed. Formaldehyde is, therefore, used as indicator of the first stage of combustion and a marker of zones with low-temperature reactions. The OH radical is formed as an intermediate during the high temperature reactions, and is used as a marker of zones where the combustion is ongoing. The purpose of the investigation was to study how the combustion process is affected by the change in homogeneity that arises from early and late injection, respectively.<br/><br>
A 0.5 liter single-cylinder optical engine equipped with a DI common rail fuel system was operated with a number of different injection timings, resulting in various levels of charge stratification. A blend of iso-octane and n-heptane was used as fuel. The measurement technique used was planar laser-induced fluorescence where formaldehyde was excited at 355nm and OH at 283nm. Two separate ICCD units were used to detect the resulting fluorescence from formaldehyde and OH. Measurement series covering the process from the start of injection until late in the expansion stroke is presented for different injection timings as well as pressure traces and emission analysis. A homogeneity index is calculated and used to compare the level of homogeneity resulting from injection timings. From early injection until about 50CAD BTDC the time, between onset of low temperature reactions and start of the high temperature reactions, is long enough for the formaldehyde to form an almost homogeneous distribution before it is being consumed. For later injection timings the high temperature reactions starts before this mixing is completed and therefore the formaldehyde distribution is not longer homogeneous and the combustion is more diesel like.},
  author       = {Collin, Robert and Nygren, Jenny and Richter, Mattias and Hildingsson, Leif and Johansson, Bengt},
  keyword      = {HCCI,Direct-Injection,Formaldehyde,OH,PLIF},
  language     = {eng},
  pages        = {311--317},
  publisher    = {ARRAY(0xa70b478)},
  series       = {[Host publication title missing]},
  title        = {Studies of the Combustion Process with Simultaneous OH- and Formaldehyde-PLIF in a Direct-Injected HCCI engine},
  year         = {2004},
}