Abstract

The influence of variations in the composition of natural gas on the ignition and combustion processes in engines is investigated. Particular attention is given to changes in the relatively small concentrations of high molar mass alkanes that may be present in the fuel. A detailed chemical kinetic scheme for the oxidation of the higher hydrocarbon components of up to n-heptane was used to investigate analytically the combustion reactions of different fuel mixtures under constant volume adiabatic conditions with initial states that are similar to those during the ignition delay of a typical internal combustion engine. These comprehensive simulation calculations require much computing capacity and time that would preclude their incorporation in full simulation models of engine processes. A simplification is introduced based on replacing artificially the small concentrations of any higher hydrocarbons that may be present in the natural gas by a kinetically equivalent amount of propane in the fuel mixture. This is done such that the resulting equivalent fuel has the same ignition delay as the original fuel under constant volume engine T.D.C. conditions. This “propane equivalent” concept was used in full engine simulation models while employing a relatively short scheme of 150 steps for the oxidation of fuel mixtures of propane, ethane, and methane in air.

Issue Section:
Internal Combustion Engines
Keywords:
internal combustion engines, ignition, combustion, fuel, gas mixtures, reaction kinetics theory, modelling
Topics:
Combustion, Engines, Fuels, Heptane, Methane, Natural gas, Temperature, Modeling, Ignition delay, Ignition, Oxidation
1.
Turner, S. H., and Weaver, C. S., 1994, “Dual Fuel Natural Gas/Diesel Engines Technology, Performance and Emissions,” Gas Research Institute Technical Report No. 0094.
2.
Vilmar, A., and Harald, V., 1996, “The Influence of Natural Gas Composition on Ignition in a Direct Injection Gas Engine Using Hot Surface Assisted Compression Ignition,” SAE Paper No. 961934.
3.
Higgin, R., and William, A., 1969, “A Shock Tube Investigation of the Ignition of Lean Methane and n-Butane Mixtures With Oxygen,” 12th Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, PA, p. 579.
4.
Lifshitz
,
A.
,
Scheller
,
K.
,
Burcat
,
A.
, and
Skinner
,
G. B.
,
1971
, “
Shock-Tube Investigation of Ignition in Methane-Oxygen-Argon Mixtures
,”
Combust. Flame
,
16
, p.
311
311
.
5.
Crossley
,
R.
,
Dorko
,
E.
,
Scheller
,
K.
, and
Burcat
,
A.
,
1972
, “
The Effect of Higher Alkanes on the Ignition of Methane-Oxygen-Argon Mixtures in Shock Waves
,”
Combust. Flame
,
19
, p.
373
373
.
6.
Frennklach
,
M.
, and
Bornside
,
E.
,
1984
, “
Shock-Initiated Ignition in Propane Mixtures
,”
Combust. Flame
,
56
, pp.
1
–
27
.
7.
Westbrook
,
C. K.
,
1979
, “
An Analytical Study of the Shock Tube Ignition of Mixtures of Methane and Ethane
,”
Combust. Sci. Technol.
,
20
, pp.
5
–
17
.
8.
Khalil, E., Samuel, P., and Karim, G. A., 1996, “An Analytical Examination of the Chemical Kinetics of the Combustion of N-Heptane-Methane Air Mixtures,” SAE Paper No. 961932.
9.
Axelsson, E. I., Brezinsky, K., Dryer, F. L., Pitz, W. J., and Westbrook, C. K., 1988, “Chemical Kinetic Modelling of the Oxidation of Large Alkane Fuels: N-Octane and Iso-Octane,” Twenty-First Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, PA, p. 783.
10.
Westbrook, C. K., and Pitz, W. J., 1988, “Detailed Kinetic Modeling of Autoignition Chemistry,” Transaction of SAE, 96, Section 7, p. 559.
11.
Westbrook, C. K., and Pitz, W. J., 1991, “Numerical Modeling of Combustion of Complex Hydrocarbon Fuels,” Numerical Approaches to Combustion Modeling (Vol. 135, Progress in Astronautics and Aeronautics), AIAA, Washington, DC, p. 57.
12.
Westbrook, C. K., 1990–1992, personal communications.
13.
Karim, G. A., Hanafi, A., and Zhou, G., 1992, “A Kinetic Investigation of the Oxidation of Low Heating Value Fuel Mixtures of Methane and Diluents,” Proceedings of the 15th Annual ASME/ETCE, Houston, TX, ASME, New York.
14.
Samuel, P., 1994, “Computational and Experimental Investigation of Ignition and Combustion of Liquid Hydrocarbon Fuels Within Homogeneous Environments of Fuel and Air,” Ph.D. dissertation, The University of Calgary.
15.
Ciezk
,
H.
, and
Adomeit
,
G.
,
1993
, “
Shock-Tube Investigation of Self-Ignition of n-Heptane-Air Mixtures Under Engine Relevant Conditions
,”
Combust. Flame
,
93
, p.
421
421
.
16.
Griffiths
,
J. F.
,
1995
, “
Reduced Kinetic Models and Their Application to Practical Combustion Systems
,”
Prog. Energy Combust. Sci.
, N. A. Chigier, ed.,
21
, Nov.,
p. 27
p. 27
.
17.
Westbrook, C. K., and Pitz, W. J., 1986, “Kinetic Modelling of Autoignition of Higher Hydrocarbons: n-Heptane, N-Octane and iso-Octane,” Complex Chemical Reaction Systems, Springer-Verlag, New York, pp. 45–62.
18.
Westbrook
,
C. K.
,
Pitz
,
W. J.
,
Thornton
,
M.
, and
Malte
,
P. C.
,
1988
, “
A Kinetic Modelling of n-Pentane Oxidation in a Well-Stirred Reactor
,”
Combust. Flame
,
72
, pp.
45
–
62
.
19.
Westbrook, C. K., and Pitz, W. J., 1991, “Numerical Modelling of a Combustion of Complex Hydrocarbon Fuels,” Numerical Approaches to Combustion Modelling (Vol. 135, Progress in Astronautics and Aeronautics), AIAA, Washington, DC, pp. 57–76.
20.
Khalil, E., 1998, “Modelling the Chemical Kinetics of Combustion of Higher Hydrocarbon Fuels in Air,” Ph.D. dissertation, University of Calgary.
Copyright © 2002
 by ASME
You do not currently have access to this content.