Ignition characteristics of dual-fuel methane-n-hexane-oxygen-diluent mixtures in a rapid compression machine and a shock tube

Abstract

Ignition delay times of methane-n-hexane-oxygen mixtures were studied experimentally and numerically in a wide temperature range (640-2335 K) using both a rapid compression machine (RCM) and a shock tube (ST). The RCM results demonstrated a two-stage ignition and negative temperature coefficient (NTC) behavior. Increasing n-hexane concentration, pressure and equivalence ratio shortened the ignition delay time. For the ST experiments, the addition of 10% n-hexane (relative to methane) can reduce the ignition delay time dramatically. However, no further reduction effect can be achieved with increasing addition of n-hexane from 10% to 20%. In addition, increasing equivalence ratio reduces the effect of n-hexane addition on ignition delay time. Three detailed chemical mechanisms, CaltechMech, GalwayMech and LLNLMech, were evaluated based on a quantitative error analysis. LLNLMech and CaltechMech demonstrated the best performance in the RCM and ST temperature ranges, respectively. Chemical kinetic analyses showed that the addition of n-hexane to methane provides some chemical pathways not available for methane oxidation which result in the production of active radicals and eventually accelerate the ignition of the methane-oxygen mixtures. The crucial intermediate species for the ignition process are H 2 O 2 and H under RCM and ST conditions, respectively.

Shock‐tube spectroscopic water measurements and detailed kinetics modeling of 1‐pentene and 3‐methyl‐1‐butene

“…The iso-branched chain is shortening significantly the delay times by 61%, 58%, and 56% for φ = 0.5, φ = 1.0, and φ = 2.0, respectively, compared with the linear isomer. To evaluate the model performances, calculations proposed by He et al 50 were performed, such as the relative error that gauges the local performance associated with each single data point, defined as:…”

“…To evaluate the model performances, calculations proposed by He et al 50 were performed, such as the relative error that gauges the local performance associated with each single data point, defined as: …”

Auto-ignition and reaction kinetic characteristics of hydrogen-enriched n-dodecane mixtures under engine-like thermodynamic conditions

“…In order to conrm the accuracy of the n-dodecane oxidation mechanism in predicting the IDT of hydrogen/n-dodecane mixtures, the IDTs of both hydrogen and n-dodecane calculated from LLNL, JetsurF 2.0, SJTU and Li mechanisms are compared to the experimental measurements from Vasu et al, 34 Mao et al 35 and Gersen et al 36 In order to select the accurate reaction mechanism to study the chemical kinetics of a hydrogen/n-dodecane mixture, error analysis of experiments and mechanisms was conducted. The calculation methods of errors are derived from He et al 43 The relative error of the ith data point, which reects the local performance of the mechanisms, is calculated as follows:…”

Development of a simplified n-heptane/methane model for high-pressure direct-injection natural gas marine engines

“…However, owing to its high-octane number and low reactivity, the natural gas is difficult to be ignited in CI engines compared to diesel fuel. As a result, when natural gas is taken as the fuel supply in CI engines, an additional ignition source like a spark plug or high-reactivity fuel should be implemented [1][2][3][4][5][6].…”

“…For natural gas, which is primarily composed of methane and minimal fractions of hydrogen, ethane, propane, or other mixtures depended on the sources and refinement methods, researchers usually adopt methane to predict the combustion process of natural gas. Many efforts have been devoted to studying the ignition process of n-heptane and methane in laboratory devices such as shock tubes [2,[16][17][18][19][20][21][22], flow reactors [23][24][25], rapid compression machines [26][27][28][29], and engines [30][31][32].…”