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This paper investigates the impact of ethanol on the oxidation of iso-octane at low and intermediate temperatures. Flow reactor experiments are conducted on binary mixtures ranging from neat iso-octane to neat ethanol at temperatures of 650 K and 875 K, a pressure of 10 bar and an equivalence ratio of 0.058, with the intermediate species and gas temperatures measured along the reactor. At 650 K, where neat iso-octane is near the peak of its low temperature chain branching, the addition of small amounts of ethanol dramatically suppresses iso-octane's reactivity and formation of intermediate species. Kinetic simulation reveals that this inhibition effect is a result of ethanol competing for OH radicals and producing an imbalance in OH formation, without affecting the iso-octane oxidation mechanism directly or altering its reaction flux distribution. By consuming more OH than it can produce, oxidation of ethanol progressively depletes OH in the radical pool, even at a low blending level, and leads to a strong reduction in the overall reactivity. In contrast, at 875 K, iso-octane and ethanol show comparable reactivities, and the formation of intermediate species correlates roughly linearly with the ethanol content, suggesting negligible interaction between the two fuels at intermediate temperatures. Overall, these results help to explain ethanol's inhibition on the knock propensity of iso-octane in spark ignition engines, as evidenced by the synergistic blending of the two fuels in octane numbers [1].

This paper presents a study of the oxidation of iso-octane, ethanol, toluene and their mixtures in a pressurised turbulent flow reactor operating at 900–930 K, 10 bar, and an equivalence ratio of 0.058. A large set of fuels is investigated, including neat iso-octane, ethanol, toluene, their binary mixtures, gasoline reference fuels (PRF91 and TRF91), and their mixtures with ethanol. The resulting species are measured along the length of the reactor and simulated using existing kinetic models from the literature. The existing models are found to reproduce measurements of the major oxidation products of iso-octane, ethanol, their binary mixtures, as well as that of PRF91 and PRF91/ethanol mixtures. However, significant differences are observed between the measurement and simulation of neat toluene. Adjustment is then made to the rate constants of key reactions in the toluene model. The adjusted model, whilst more accurately reproducing neat toluene oxidation, does not significantly improve the modelling of toluene containing mixtures. This suggests that further investigations should focus on the oxidation of neat toluene, as well as the chemical interactions of toluene containing mixtures.

This paper studies the oxidation of n-heptane, iso-octane, ethanol and their mixtures in a pressurized flow reactor, with a focus on the potential relation between the fuels oxidation reactivity and their octane ratings. The flow reactor experiments are conducted at 550–900 K, 10 bar and an equivalence ratio of 0.058. Carbon monoxide is measured as an indicator of the global reactivity. Evident low temperature oxidation and negative temperature coefficient (NTC) behaviors are observed for n-heptane and iso-octane over a similar temperature window (600–800 K). Ethanol, on the other hand, shows negligible reactivity up to 800 K but produces a substantial amount of CO above 850 K indicating significantly higher reactivity than iso-octane. Oxidation of these fuels is then classified into low temperature oxidation (LTO), NTC, intermediate temperature oxidation (ITO), and high temperature oxidation (HTO) regimes. A systematic study is then conducted on primary reference fuels (PRFs) and ethanol/iso-octane mixtures. PRFs show approximately linear blending in terms of CO formation in the LTO, NTC, and ITO regimes, which is consistent with the definition of the octane number scale. In contrast, adding ethanol into iso-octane disproportionally inhibits the CO formation over the same temperature range, with 20 vol% of ethanol completely suppressing the reactivity of iso-octane. Such behavior is also consistent with the synergistic octane blending of the two compounds recently reported [Foong et al. Fuel 115 (2014) 727–739]. These results suggest a potential connection between the oxidation reactivity of these fuels and their octane blending behaviors. Kinetic modeling is conducted using the latest combustion mechanisms for neat compounds and gasoline surrogate. Good agreement in CO formation is observed between the model and experiment for both neat fuels and their mixtures.

This work investigates the oxidation of hydrogen near its second explosion limit in a turbulent flow reactor at pressures of 1 to 8 bar, temperatures of 950 K and an equivalence ratio of 0.035. The concentrations of H2, O2 and H2O are measured along the reactor and simulated using several kinetic models from the literature. These experiments demonstrate evident negative pressure dependence from roughly 1 to 4 bar, with further increases in pressure resuming its positive impact on reaction rates. The simulated and measured species concentrations along the reactor generally agree within a factor of 2. Further investigation is then conducted to measure the rate coefficient of reaction H + O2 (+ M) = HO2 (+M) (R2), which is one of the most sensitive reactions in hydrogen's oxidation chemistry at these conditions. This investigation is conducted by using nitric oxide (NO) as a dopant and measuring the resulting, quasi-steady-state concentrations of NO2. The rate coefficients are obtained at 950 – 1010 K. Combined with literature results, an Arrhenius expression is proposed, k 2 , 0 N 2 = 4.50 × 1020 (T/K)−1.73 [cm6 mole−2 s−1], for the reaction rate at the low-pressure limit over 500 K – 2000 K with N2 as the bath gas. Simulations using the models from the literature with the proposed Arrhenius expression for this reaction then demonstrate improved agreement with the experiments.

A plug flow reactor (PFR) is built for investigating the oxidation chemistry of fuels at up to 50 bar and 1000 K. These conditions include those corresponding to the low temperature combustion (i.e. the autoignition) that commonly occurs in internal combustion engines. Turbulent flow that approximates ideal, plug flow conditions is established in a quartz tube reactor. The reacting mixture is highly diluted by excess air to reduce the reaction rates for kinetic investigations. A novel mixer design is used to achieve fast mixing of the preheated air and fuel vapour at the reactor entrance, reducing the issue of reaction initialization in kinetic modelling. A water-cooled probe moves along the reactor extracting gases for further analysis. Measurement of the sampled gas temperature uses an extended form of a three-thermocouple method that corrects for radiative heat losses from the thermocouples to the enclosed PFR environment. Investigation of the PFR's operation is first conducted using non-reacting flows, and then with isooctane oxidation at 900 K and 10 bar. Mixing of the non-reacting temperature and species fields is shown to be rapid. The measured fuel consumption and CO formation are then closely reproduced by kinetic modelling using an extensively validated iso-octane mechanism from the literature and the corrected gas temperature. Together, these results demonstrate the PFR's utility for chemical kinetic investigations.