Autoignition behavior of gasoline/ethanol blends at engine-relevant conditions

Abstract

Ethanol is an attractive oxygenate increasingly used for blending with petroleum-derived gasoline yielding beneficial combustion and emissions behavior for a range of internal combustion engine schemes, including stoichiometric spark-ignition and low temperature combustion (LTC). As such, it is important to fundamentally understand the autoignition behavior of gasoline/ethanol blends. This work utilizes a rapid compression machine (RCM) and a homogeneous charge compression ignition (HCCI) engine to experimentally quantify changes in fuel reactivity, through ignition delay times and preliminary heat release, for blends of 0 to 30% vol./vol. into a full boiling range research gasoline (FACE-F). Diluted/stoichiometric and undiluted/fuel-lean conditions are explored covering a wide range of compressed temperatures and pressures relevant to conventional and advanced, gasoline combustion engines. Detailed chemical kinetic modeling is undertaken using a recently updated gasoline surrogate model in conjunction with a five-component surrogate to model the RCM experiments and provide chemical insight into the perturbative effects of ethanol on the autoignition process. The diluted/stoichiometric RCM measurements reveal that within the low-temperature regime ethanol retards first-stage and main ignition delay times, and suppresses both the rates and extents of low-temperature heat release (LTHR), while within the intermediate-temperature regime ethanol only causes slight changes. Good agreement of ignition delay time and preliminary heat release prediction is found between model and experimental results. Sensitivity and flux analyses further show that ethanol blending effects are dominated by the competition between the H-atom abstraction from ethanol and other fuel components by OH radical at low temperatures and by HO2 radical at intermediate temperatures. These findings are consistent 3 across both fuel loading conditions explored in this study. In addition, when HCCI engine experiments are mapped onto undiluted/lean RCM measurements under a constant combustion phasing scenario, good correspondence between the two apparatuses is observed for LTHR and start of high-temperature heat release. The current study highlights the importance of characterizing LTHR in predicting fuel behaviors in high-boost/low-temperature engines, and demonstrates that RCM experiments can provide an alternative, and more-efficient avenue for such characterization.

Knock-limited combustion of ethanol-, isobutanol-, and 2-methyl-3-buten-2-ol-gasoline blends in a direct-injected spark-ignition engine

“…At the highest pressures, shown in Figure 16(d), M56 continues to display no evidence of PSHR. Ethanol addition has been shown to reduce the amount of low temperature heat release in other studies 50,51 and that observation is mirrored here. However, comparatively, M56 appears to reduce PSHR beyond that of E30 for the loads tested here.…”

An experimental and kinetic modeling study of the ignition delay and heat release characteristics of a five component gasoline surrogate and its blends with iso‐butanol within a rapid compression machine

“…There is little real‐world experimental data from fundamental experiments (such as from RCMs) available, which could help to quantify preliminary exothermicity events such as LTHR and ITHR. Heat release analyses such as those produced in this study and others 54,82,83 provide an opportunity for this and for the improvement of kinetic models by serving as an additional validation target. The current work shows that the chosen model fails to reproduce the experimentally derived heat release profiles to lesser or greater extents in different temperature regions, and that this failure may underlie further global model failures, such as the overprediction of reactivity.…”

Experimental and Kinetic Modeling Study of 3-Methyl-2-butenol (Prenol) Oxidation

“…These IDTs were simulated using the kinetic model developed in this work with the Chemkin Pro software and ZeroRK. , The ignition event in the simulations is defined as the time of maximum pressure rise due to ignition. For the HPST measurements, the simulations assume constant volume conditions, while for RCM measurements volume/time histories from nonreactive experiments in which the O 2 content is replaced with N 2 were used in our simulations to account for effects of the compression stroke and heat losses after compression.…”