A chemical kinetically based ignition delay correlation for iso-octane covering a wide range of conditions including the NTC region
- Department of Mechanical Engineering, Marquette University, Milwaukee, WI 53201-1881 (United States)
An ignition delay correlation has been developed for iso-octane based on the functional behavior exhibited by a detailed chemical kinetic mechanism. The correlation employs a traditional Arrhenius-based, power law formulation, {tau}=A{phi}{sup {alpha}}p{sup {beta}}{chi}{sub O{sub 2}}{sup {gamma}} x exp ({lambda}), including dependencies for equivalence ratio ({phi}), pressure (p) and oxygen percentage ({chi}{sub O2}). However the exponents for these parameters, {alpha}, {beta}, and {gamma}, respectively, are expressed as third-order polynomials with respect to temperature in order to capture changes in functionality seen across different regimes. At very low temperatures {alpha}, {beta}, and {gamma} are forced to a constant value, as seen within the mechanism. The activation energy term, {lambda}, is written as a combination of two quadratic expressions so that the behavior in the negative temperature coefficient (NTC) region can be captured. A pressure-dependent term is also included in the expression for {lambda} in order to reduce the activation energy at higher pressures in the NTC region due to increased low temperature reactivity, and the appearance of cool flame, or low temperature heat release (LTHR). The resulting expression contains 37 constants. The new correlation is applicable over a wide range of conditions and can be used for data comparisons and mechanism evaluation, as well as systems-level engineering simulations. In this work experimental data from rapid compression machines (RCM) and shock tubes (ST) are compared through normalizing features of the correlation, and the performance of a detailed kinetic mechanism is evaluated based on the functional behavior of the {alpha}, {beta}, {gamma} and {lambda} parameters. Six hundred and sixty-one (661) data points have been used to fit the 37 constants of the expression where the experimental conditions cover {phi}=0.2-2.0, p=1-60atm, {chi}{sub O{sub 2}} and T=650-2000 K. Data normalized through the correlation indicate a standard deviation of {+-}4%. Departures from the correlation can be attributed to an incomplete description of the functional dependencies, some inconsistencies with regard to diluent composition, experimental uncertainties, and facility-influenced phenomena. The experimental points have also been simulated using the LLNL detailed iso-octane mechanism, where the computed ignition delay times have been fit to the new correlation. Agreement and differences between the correlated experimental and simulation {alpha}, {beta}, {gamma} and {lambda} functions are highlighted, where it is noted that there is a substantial discrepancy concerning the increased low temperature chemistry at high pressure. Implications for future engine design are discussed. (author)
- OSTI ID:
- 21177449
- Journal Information:
- Combustion and Flame, Vol. 156, Issue 6; Other Information: Elsevier Ltd. All rights reserved; ISSN 0010-2180
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
33 ADVANCED PROPULSION SYSTEMS
OCTANE
PRESSURE RANGE MEGA PA 10-100
ISO
TEMPERATURE RANGE 0400-1000 K
CORRELATIONS
IGNITION
ACTIVATION ENERGY
COMPARATIVE EVALUATIONS
EXPERIMENTAL DATA
POLYNOMIALS
TEMPERATURE RANGE 1000-4000 K
OXYGEN
SIMULATION
TEMPERATURE COEFFICIENT
HEAT
PRESSURE DEPENDENCE
DESIGN
ENGINES
PERFORMANCE
TIME DELAY
PRESSURE RANGE KILO PA
Iso-octane
Ignition delay