A Multi-Component Blend as a Diesel Fuel Surrogate for Compression Ignition Engine Applications

Abstract

A mixture of n-dodecane and m-xylene is investigated as a diesel fuel surrogate for compression ignition engine applications. Compared to neat n-dodecane, this binary mixture is more representative of diesel fuel because it contains an alkyl-benzene which represents an important chemical class present in diesel fuels. A detailed multi-component mechanism for n-dodecane and m-xylene was developed by combining a previously developed n-dodecane mechanism with a recently developed mechanism for xylenes. The xylene mechanism is shown to reproduce experimental ignition data from a rapid compression machine and shock tube, speciation data from the jet stirred reactor and flame speed data. This combined mechanism was validated by comparing predictions from the model with experimental data for ignition in shock tubes and for reactivity in a flow reactor. The combined mechanism, consisting of 2885 species and 11754 reactions, was reduced to a skeletal mechanism consisting 163 species and 887 reactions for 3D diesel engine simulations. The mechanism reduction was performed using directed relation graph (DRG) with expert knowledge (DRG-X) and DRG-aided sensitivity analysis (DRGASA) at a fixed fuel composition of 77% of n-dodecane and 23% m-xylene by volume. The sample space for the reduction covered pressure of 1–80 bar, equivalence ratio of 0.5–2.0, and initial temperature of 700–1600 K for ignition. The skeletal mechanism was compared with the detailed mechanism for ignition and flow reactor predictions. Finally, the skeletal mechanism was validated against a spray flame dataset under diesel engine conditions documented on the Engine Combustion Network (ECN) website. These multi-dimensional simulations were performed using a Representative Interactive Flame (RIF) turbulent combustion model. Encouraging results were obtained compared to the experiments with regards to the predictions of ignition delay and lift-off length at different ambient temperatures.

Experimental and numerical study of lift-off length and ignition delay of a two-component diesel surrogate

“…Thereafter Pei et al [13] extended the mRIF implementation for the multi-component SR23 mixture by using the reduced chemical kinetic model consisting of 163 species and 887 reactions. The reduced mechanism was extensively compared to the detailed mechanism by Pei et al [13].…”

“…Thereafter Pei et al [13] extended the mRIF implementation for the multi-component SR23 mixture by using the reduced chemical kinetic model consisting of 163 species and 887 reactions. The reduced mechanism was extensively compared to the detailed mechanism by Pei et al [13]. Following the recommendations from Kundu et al [33] and Pei et al [13], more than 20 flamelets were used in the simulations, keeping in mind both computational accuracy and wall-clock times since higher number of flamelets typically increase the computational cost.…”

“…CFD simulations were performed utilizing a multi-flamelet representative interactive flamelet (mRIF) combustion model described by the authors [13]. A reduced mechanism to mimic the combustion characteristics of the two-component mixture was first reduced and then validated under a limited set of ambient temperature conditions by the authors [13]. The second major objective of the current study is to further evaluate this simulation approach over a wide parametric range of injection and ambient conditions.…”

“…The detailed chemical mechanism of the binary mixture has 2885 species, compared to the pure n-dodecane with 2115 species, due to the inclusion of m-xylene. In order to be computationally tractable, significant reduction was performed on the detailed mechanism in our previous study [13] while still maintaining the high chemical fidelity. The final reduced mechanism has 163 species and 887 reactions and has been validated extensively at different conditions.…”

“…The availability of such a robust and unique data-set provides a more effective crucible for model validation. CFD simulations were performed utilizing a multi-flamelet representative interactive flamelet (mRIF) combustion model described by the authors [13]. A reduced mechanism to mimic the combustion characteristics of the two-component mixture was first reduced and then validated under a limited set of ambient temperature conditions by the authors [13].…”