A Global Reaction Model for the HCCI Combustion Process

Abstract

This paper presents a new global reaction model to simulate the Homogeneous Charge Compression Ignition (HCCI) combustion process. The model utilizes seven equations and seven active species. The model includes five reactions that represent degenerate chain branching in the low temperature region, including chain propagation, termination and branching reactions and the reaction of HOOH at the second stage ignition. Two reactions govern the high temperature oxidation, to allow formation and prediction of CO, CO 2 , and H 2 O. Thermodynamic parameters were introduced through the enthalpy of formation of each species. We were able to select the rate parameters of the global model to correctly predict the autoignition delay time at constant density for n-heptane and iso-octane, including the effect of equivalence ratio. Keeping the same reactions and rate parameters, simulations were compared with measured and calculated data from our engine operating at the following conditions: speed-750 RPM, inlet temperature-393 K to 453 K, fuel-PRF 20, equivalence ratio-0.4 and 0.5, and volumetric efficiency-71% and 89%. The simulations are in good agreement with the experimental data for this initial set of runs using PRF 20, including temperature, pressure, ignition delay, combustion duration, and heat release.

A Zero-Dimensional Combustion Model with Reduced Kinetics for SI Engine Knock Simulation

“…Note that the mass burned due to chemical kinetic reactions will only play a significant part when auto ignition starts. This is expressed as (8) where t Δ is the calculation time step, subscript j is the step number, i is species number where 1 denotes fuel, 2 denotes O 2 and 3 denotes N 2 .…”

“…These are generally categorized into detailed [1,2], lumped [3], reduced [4,5,6], and global models [7,8] according to the numbers of the reactions and the species [9]. The detailed chemical kinetic mechanisms were developed mostly by adjusting reaction rate parameters and thermal chemical data to fit experimental data.…”

Global reaction mechanism for the auto-ignition of full boiling range gasoline and kerosene fuels

“…The balance between the forward and backward rate of this reaction is very sensitive to the fuel composition and pressure. This explains, why Zheng et al [38] originally introduced the fuel specific constant C 3+ and an explicit pressure dependence in the respective reaction rate expressions. A critical reaction for the transition from the NTC regime to the intermediate temperature region and ultimately the second stage ignition is the branching reaction of H 2 O 2 .…”

“…The latter can be attributed to the absence of competition between a branching and non-branching reaction path, a prerequisite to capture NTC behaviour. To account for this competition, Zheng et al [38] recently extended the Schreiber model, introducing an additional intermediate, stable up to the main ignition stage. The resulting 7-step reaction scheme successfully predicted main ignition timing and overall HCCI behaviour at different operating conditions, but the heat release and temperature jump due to first-stage (cool flame) ignition, as experimentally observed, were still not captured.…”

“…As discussed in [38] and [39], the high temperature chemistry is embodied in the first two reactions, whereas the low and intermediate temperature phenomena are described by reactions 3 to 5. The correlation between the latter reactions and the detailed chemistry explained in the previous section is illustrated in Figure 2.…”