Autoignition of n-butanol at elevated pressure and low-to-intermediate temperature

Abstract

Autoignition experiments for n-butanol have been performed using a heated rapid compression machine at compressed pressures of 15 and 30 bar, in the compressed temperature range of 675-925 K, and for equivalence ratios of 0.5, 1.0, and 2.0. Over the conditions studied, the ignition delay decreases monotonically as temperature increases, and the autoignition response exhibits single-stage characteristics. A non-linear fit to the experimental data is performed and the reactivity, in terms of the inverse of ignition delay, shows nearly second order dependence on the initial oxygen mole fraction and slightly greater than first order dependence on initial fuel mole fraction and compressed pressure. Experimentally measured ignition delays are also compared to simulations using several reaction mechanisms available in the literature. Agreement between simulated and experimental ignition delay is found to be unsatisfactory. Sensitivity analysis is performed on one recent mechanism and indicates that uncertainties in the rate coefficients of parent fuel decomposition reactions play a major role in causing the poor agreement. Path analysis of the fuel decomposition reactions supports this conclusion and also highlights the particular importance of certain pathways. Further experimental investigations of the fuel decomposition, including speciation measurements, are required.

On the uncertainty of temperature estimation in a rapid compression machine

“…This approach to mixture preparation has been validated in several previous studies by withdrawing gas samples from the mixing tank and analyzing the contents by GC/MS [14], GC-FID [20], and GC-TCD [21]. The study of Weber et al [14] verified that the mole fraction of fuel was within 5 % of the expected mole fraction and the study of Das et al [21] verified that the mole fraction of water was within 2 % of the expected value.…”

“…Such analyses have been conducted in the past, for example in the work of Weber et al [14] and Mittal and Sung [15]. Previous analyses generally assumed that the uncertainty of each parameter was normally distributed and independent (i.e.…”

Using rapid compression machines for chemical kinetics studies

“…In this approach, continuous stirring is needed to ensure a homogeneous mixture, for instance by using a magnetic stirrer [cf. 44,65,[70][71][72][73][74][75]. In addition, the possibility of fuel cracking/pyrolysis within the mixture preparation vessel over an extended time period needs to be avoided, and characterization experiments should be conducted to confirm the assumptions of minimal/negligible fuel loss, mixture homogeneity, and non-decomposition of fuel in the mixture preparation vessel, as carried out in [e.g., 65,73,74].…”

“…An error propagation analysis is needed to determine the contributions of 37 these factors to the uncertainty of the calculation of the compressed temperature. Weber et al [73] reported that the largest contributor to the total uncertainty in compressed temperature is the error in the initial pressure measurement, whereas the contributions from the measurements of the initial temperature and the compressed pressure are less significant. In addition, the uncertainty of T C is dependent on the actual value of the initial pressure, but not on the values of the other quantities [73].…”

Design of synthetic EGR and simulation study of the effect of simplified formulations on the ignition delay of isooctane and n-heptane

“…The present work is justified because of the great amount of studies where the auto-ignition of different fuels at low temperatures is analyzed. In them, the ignition delay is obtained in environments poor in oxygen, and the dilution is done by adding N 2 , Ar or CO 2 indistinctly [32][33][34]. This way to control the percent of oxygen is very useful to obtain ignition delays at different temperatures and pressures, and with different combustion temperatures.…”