Abstract
AbstractThis study investigates the performance of a five component gasoline surrogate (iso‐octane, toluene, n‐heptane, 1‐hexene, and ethanol) in representing the ignition delay time (IDT) behavior of gasoline (reference gasoline PR5801—research octane number 95.4, motor octane number 86.6), at conditions of 675–870 K, 20 bar, and Ф = 1 (stoichiometric) within a rapid compression machine (RCM). Experimentally, the surrogate produces a good representation of the ignition behavior of the gasoline at these conditions, displaying a similar IDT profile. The influence of blending with iso‐butanol on the surrogate's ignition delay behavior is also investigated, at blends from 5% to 70% of iso‐butanol by volume. The surrogate continues to produce a reasonable representation of the experimental IDTs of gasoline and iso‐butanol blends, except under a high degree of iso‐butanol blending (50% iso‐butanol), where the surrogate produced longer IDTs, particularly at temperatures below 740 K. Blends of 5% and 10% iso‐butanol produce IDTs shorter than that of any other blend, including the “neat” surrogate, at temperatures of 740–770 and 830 K, respectively. Kinetic modeling of RCM IDTs is performed using CHEMKIN‐PRO (Reaction Design: San Diego, CA, 2011) and a combined mechanism of the Sarathy et al. butanol isomers mechanism (Progress in Energy and Combustion Science 2014; 44: 40–102) and Lawrence Livermore National Laboratories “Gasoline Surrogate” mechanism (Proceedings of the Combustion Institute 2011; 33(1): 193–200). The model produces good IDT predictions below 740 K but overpredicts reactivity in the negative temperature coefficient region. Heat release rate analysis is conducted for experimental and modeling results to investigate low‐temperature heat release (LTHR) behavior. Simulations largely fail to accurately reproduce this behavior. This analysis, combined with local OH and brute force Δhf sensitivity analyses, indicates the significance of LTHR in the determination of IDTs and provides RCM heat release rates for future model validation.
Highlights
Bio-derived fuels, including bioalcohols, have emerged as attractive alternatives to fossil-derived fuels, either as single fuels or as blending components
At the lower end of the temperature regime, the model slightly overpredicts the ignition delay time (IDT) of the 5-C surrogate. These differences indicate that the combined mechanism applied does not accurately reproduce the ignition behavior of one or multiple of the 5-C surrogate components. This misrepresentation is investigated further in this study, through the application of sensitivity analysis techniques since it is likely to be due to uncertainties in reaction rate parameters, and species thermodynamic data for fuel component related species that have been calculated through group additivity (GA)
The blending of iso-butanol with a 5-C gasoline surrogate produced interesting nonlinear responses in terms of measured IDTs at low iso-butanol concentrations, similar to those previously observed for n-butanol blending.[28]
Summary
Bio-derived fuels, including bioalcohols, have emerged as attractive alternatives to fossil-derived fuels, either as single fuels or as blending components. The attractiveness of alcohols in this case is due in part to the physical and thermodynamic similarities they share with conventional fossil fuels, such as gasoline This allows for possible applications in spark-ignition (SI) engine technologies and fuel distribution infrastructure with little to no modification.[1,2] It is common for ethanol to be used in such a way, blended in low amounts with gasoline before reaching the end consumer. The feasibility of a given blend is dependent on satisfying engine performance concerns, such as a fuel’s knock resistance This is important for use in current SI engines and for emergent technologies such as turbo-charged, downsized engines, and homogeneous compression charge ignition (HCCI) engines
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