scholarly journals Controlling n-Heptane HCCI Combustion With Partial Reforming: Experimental Results and Modeling Analysis

2009 ◽  
Vol 131 (5) ◽  
Author(s):  
Vahid Hosseini ◽  
W. Stuart Neill ◽  
M. David Checkel
Keyword(s):  
Low Temperature ◽  
Heat Release ◽  
Temperature Coefficient ◽  
Negative Temperature Coefficient ◽  
Negative Temperature ◽  
Hydrocarbon Fuel ◽  
Delay Period ◽  
Experimental Results ◽  
Dual Fuel ◽  
Auto Ignition

One potential method for controlling the combustion phasing of a homogeneous charge compression ignition (HCCI) engine is to vary the fuel chemistry using two fuels with different auto-ignition characteristics. Although a dual-fuel engine concept is technically feasible with current engine management and fuel delivery system technologies, this is not generally seen as a practical solution due to the necessity of supplying and storing two fuels. Onboard partial reforming of a hydrocarbon fuel is seen to be a more attractive way of realizing a dual-fuel concept, while relying on only one fuel supply infrastructure. Reformer gas (RG) is a mixture of light gases dominated by hydrogen and carbon monoxide that can be produced from any hydrocarbon fuel using an onboard fuel processor. RG has a high resistance to auto-ignition and wide flammability limits. The ratio of H2 to CO produced depends on the reforming method and conditions, as well as the hydrocarbon fuel. In this study, a cooperative fuel research engine was operated in HCCI mode at elevated intake air temperatures and pressures. n-heptane was used as the hydrocarbon blending component because of its high cetane number and well-known fuel chemistry. RG was used as the low cetane blending component to retard the combustion phasing. Other influential parameters, such as air/fuel ratio, EGR, and intake temperature, were maintained constant. The experimental results show that increasing the RG fraction retards the combustion phasing to a more optimized value causing indicated power and fuel conversion efficiency to increase. RG reduced the first stage of heat release, extended the negative temperature coefficient delay period, and retarded the main stage of combustion. Two extreme cases of RG composition with H2/CO ratios of 3/1 and 1/1 were investigated. The results show that both RG compositions retard the combustion phasing, but that the higher hydrogen fraction RG is more effective. A single-zone model with detailed chemical kinetics was used to interpret the experimental results. The effect of RG on combustion phasing retardation was confirmed. It was found that the low temperature heat release was inhibited by a reduction in intermediate radical mole fractions during low temperature reactions and during the early stages of the negative temperature coefficient delay period.

scholarly journals Controlling n-Heptane HCCI Combustion With Partial Reforming: Experimental Results and Modeling Analysis

2008 ◽  
Author(s):  
Vahid Hosseini ◽  
W. Stuart Neill ◽  
M. David Checkel
Keyword(s):  
Low Temperature ◽  
Heat Release ◽  
Temperature Coefficient ◽  
Negative Temperature Coefficient ◽  
Negative Temperature ◽  
Hydrocarbon Fuel ◽  
Delay Period ◽  
Experimental Results ◽  
Dual Fuel ◽  
Auto Ignition

One potential method for controlling the combustion phasing of a Homogeneous Charge Compression Ignition (HCCI) engine is to vary the fuel chemistry using two fuels with different auto-ignition characteristics. Although a dual-fuel engine concept is technically feasible with current engine management and fuel delivery system technologies, this is not generally seen as a practical solution due to the necessity of supplying and storing two fuels. Onboard partial reforming of a hydrocarbon fuel is seen to be a more attractive way to realize a dual-fuel concept while relying on only one fuel supply infrastructure. Reformer Gas (RG) is a mixture of light gases dominated by hydrogen and carbon monoxide that can be produced from any hydrocarbon fuel using an onboard fuel processor. RG has a high resistance to auto-ignition and wide flammability limits. The ratio of H2 to CO produced depends on the reforming method and conditions, as well as the hydrocarbon fuel. In this study, a CFR engine was operated in HCCI mode at elevated intake air temperatures and pressures. n-heptane was used as the hydrocarbon blending component because of its high cetane number and well-known fuel chemistry. RG was used as the low cetane blending component to retard the combustion phasing. Other influential parameters such as air/fuel ratio, EGR, and intake temperature were maintained constant. The experimental results show that increasing the RG fraction retards the combustion phasing to a more optimized value causing indicated power and fuel conversion efficiency to increase. RG reduced the first stage of heat release, extended the negative temperature coefficient delay period, and retarded the main stage of combustion. Two extreme cases of RG composition with H2/CO ratios of 3/1 and 1/1 were investigated. The results show that both RG compositions retard the combustion phasing, but that the higher hydrogen fraction RG is more effective. A single-zone model with detailed chemical kinetics was used to interpret the experimental results. The effect of RG on combustion phasing retardation was confirmed. It was found that the low temperature heat release was inhibited by a reduction of intermediate radical mole fractions during low temperature reactions and the early stages of the negative temperature coefficient delay period.

Investigations of Low-Temperature Heat Release and Negative Temperature Coefficient Regions of Iso-Paraffinic Kerosene in a Constant Volume Combustion Chamber

2021 ◽  
Author(s):  
Valentin Soloiu ◽  
Richard Smith ◽  
Amanda Weaver ◽  
Drake Grall ◽  
Cesar Carapia ◽  
...  
Keyword(s):  
Low Temperature ◽  
Heat Release ◽  
Combustion Chamber ◽  
Temperature Coefficient ◽  
Ignition Delay ◽  
Negative Temperature Coefficient ◽  
Negative Temperature ◽  
Fuel Blends ◽  
Temperature Heat ◽  
Constant Volume Combustion Chamber

Abstract Research was conducted to observe the correlation of ignition delay, combustion delay, the negative temperature coefficient region (NTCR), and the low temperature heat release region (LTHR), in a constant volume combustion chamber (CVCC) in relation to blended amounts of iso-paraffinic kerosene (IPK) by mass with Jet-A and their derived cetane numbers (DCN). The study utilizes the ASTM standard D7668-14.a in a PAC CID 510 CVCC. The DCN was calculated using the ignition delay and combustion delay measured over 15 combustion events. The fuel blends investigated were 75%Jet-A blended with 25%IPK, 50%Jet-A with 50%IPK, 25%Jet-A with 75%IPK, neat Jet-A, and neat IPK. The ignition delay of neat Jet-A and IPK was found to be 3.26ms and 5.31ms, respectively, and the combustion delay of the fuels were 5.00ms and 17.17 ms, respectively. The ignition delay for 75Jet-A25IPK, 50Jet-A50IPK, 25Jet-A75IPK, fuel blends were found to be 3.5ms, 3.8ms, and 4.2ms, respectively. The combustion delay between the 75Jet-A25IPK, 50Jet-A50IPK, 25Jet-A75IPK, blends are 5.8ms, 7.0ms, and 9.4ms, respectively. The DCNs for 75Jet-A25IPK, 50Jet-A50IPK, 25Jet-A75IPK 43.1, 38.7, and 33.5, respectively. The DCN of the fuel blends compared to neat Jet-A was lower by 10.16% for 75Jet-A25IPK, 19.37% for 50Jet-A50IPK, 30.50% for 25Jet-A75IPK and 46.03% for neat IPK. Blends with larger amounts by mass of IPK resulted in extended ignition and combustion delays. It is concluded that the fuels that have larger amounts of IPK blended within them have extended NTC regions, LTHR regions, and decreased ringing intensity during combustion.

High performance and negative temperature coefficient of low temperature hydrogen gas sensors using palladium decorated tungsten oxide

2015 ◽  
Vol 3 (3) ◽  
pp. 1317-1324 ◽  
Author(s):  
Yanrong Wang ◽  
Bin Liu ◽  
Songhua Xiao ◽  
Han Li ◽  
Lingling Wang ◽  
...  
Keyword(s):  
Low Temperature ◽  
Temperature Coefficient ◽  
Gas Sensors ◽  
High Performance ◽  
Negative Temperature Coefficient ◽  
Solvothermal Method ◽  
Negative Temperature ◽  
Hydrogen Sensor ◽  
Hydrogen Gas ◽  
Hydrogen Gas Sensors

A catalytically activated hydrogen sensor is obtained based on Pd decorated WO3 nanoplates constructed by a solvothermal method.

Low temperature dielectric properties and NTCR behavior of the BaFe0.5Nb0.5O3 double perovskite ceramic

2020 ◽  
Vol 22 (5) ◽  
pp. 2986-2998 ◽  
Author(s):  
Vijay Khopkar ◽  
Balaram Sahoo
Keyword(s):  
Dielectric Properties ◽  
Low Temperature ◽  
Temperature Coefficient ◽  
Negative Temperature Coefficient ◽  
Double Perovskite ◽  
Negative Temperature ◽  
Lead Free ◽  
Temperature Coefficient Of Resistance ◽  
Perovskite Ceramic

The microstructure and low-temperature dielectric properties of lead-free BaFe0.5Nb0.5O3 ceramics exhibiting a negative temperature coefficient of resistance behavior.

The Master Equation for the Dissociation of a Dilute Diatomic Gas. X. How Rotation Causes Low Arrhenius Temperature Coefficients

1973 ◽  
Vol 51 (18) ◽  
pp. 3152-3155 ◽  
Author(s):  
Huw O. Pritchard
Keyword(s):  
Low Temperature ◽  
Temperature Coefficient ◽  
Rate Constants ◽  
Recombination Rate ◽  
Negative Temperature Coefficient ◽  
Negative Temperature ◽  
Equilibrium Form ◽  
Temperature Coefficients ◽  
Recombination Rate Constant ◽  
Arrhenius Temperature

It is shown that previously calculated nonequilibrium rate constants for the dissociation of H2 and D2 appear to approach a rotationally averaged equilibrium expression at low temperature. This equilibrium form of the rate expression itself has an Arrhenius temperature coefficient for dissociation which is significantly less than the dissociation energy, and the corresponding recombination rate constant has a negative temperature coefficient. The reasons for this are explained.

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