Effects of Exhaust Gas Dilution on the Laminar Burning Velocity of Real-World Gasoline Fuel Flame in Air

Abstract

The effects of exhaust gas recirculation (EGR) on the laminar burning velocity of a commercial gasoline fuel-air mixture have been studied both numerically as well as experimentally at atmospheric pressure. The experiments have been performed using the heat flux burner method. For numerical simulation, a binary mixture of 95% iso-octane and 5% n-heptane (PRF95) is assumed to be the surrogate for the real world gasoline fuel. The numerical simulations have been carried out using a skeletal mechanism comprising of 171 species and 861 reactions for primary reference fuels. A correlation of laminar burning velocity of the commercial fuel is suggested based on experimental data for different EGR dilutions. The results show that the reduction in the laminar burning velocity caused by the EGR dilution can be recovered by the increase in the unburnt gas temperature. However, the rise in the unburnt gas temperature results in a trivial rise in the adiabatic flame temperature. The increase in the laminar burning velocity due to elevated unburnt gas temperature is principally attributed to the increase in thermal diffusivity of the fuel-air mixture, while the reaction rate has only a minor influence. The presence of CO 2 in the EGR influences the chemistry of the flame along with diluting it. Under stoichiometric conditions, the chemical and dilution effects toward the reduction in laminar burning velocity are almost equal.

Modeling laminar burning velocity of gasoline using an energy fraction-based mixing rule approach

“…Similar correlations were reported in the literature, for example, 1 − 2 . 5 Y dil for 0–30% mass fraction of diluent by Ryan and Lestz, 20 and 1 − 2 . 06 V dil 0 . 73 for 0–30% volume fraction of diluent by Rhodes and Keck. 41 Recently, Bhattacharya et al 21 measured LBVs of gasoline-air flame in the equivalence ratio range of 0.7–1.3 by adding an inert gas up to 25% under T 0 = 423 K and p = 1 atm conditions, and formulated a quartic equation to model the diluent effect on LBV. Although the equation was complex compared to the previous correlations, it resulted in an average coefficient of 2.2 which was similar to them.…”

“…It is worth noting that the diluent effect was referred to the correlation proposed by Metghalchi and Keck 10 because of the consistent experimental findings in the literature. 8,10,20,21 The developed LBV model was validated using the measurement data of the LBV of gasoline found in the literature, and the model was applied to the CFD simulations of DISI engine under the various operating conditions to explore its prediction capability.…”

A Comparison of EGR Correction Factor Models Based on SI Engine Data

“…The article introduces a new method to determine correction factors for exhaust gas recirculation (EGR) from engine pressure trace data by using a reverse thermodynamic model. Using this approach, a new correlation for the effects of exhaust gas diluent on the laminar burning velocity of a EURO VI specification gasoline is derived and compared against existing models by Metghalchi and Keck [10], Rhodes and Keck [11], Fu et al [12] and Bhattacharya et al [14]. It is found that existing models tend to overestimate the impact of EGR on laminar burning velocity, probably because their derivation did not consider all chemical species contained in exhaust gas.…”

“…The most recently suggested correction factor is based on a combination of simulations and experiments. Bhattacharya et al [14] used a commercial gasoline (Shell V-Power as available in Germany) that, given the publication date of the paper, should be compliant with EURO VI regulations. For the experimental data, Bhattacharya et al used a heat flux burner to determine the stretch free laminar burning velocities with the diluent comprising of carbon dioxide and nitrogen.…”

Experimental and Numerical Investigation of the CO2 Dilution Effect on Laminar Burning Velocities and Burned Gas Markstein Lengths of High/Low RON Gasolines and Isooctane Flames at Elevated Temperatures

“…Jerzembeck et al 30 employed the spherically expanding flames under a constant pressure approach to understand how laminar burning velocities of standard gasoline at 10−25 bar and 373 K are affected by N 2 dilution. Lastly, Bhattacharya et al 31 measured the laminar flame speeds of gasoline/air mixtures diluted with N 2 at 423 K and 1 bar with a heat flux burner.…”