Detailed N-heptane Research Articles

Chemistry of Ammonia/Hydrogen and Ammonia/n-Heptane Fuels: Reaction Mechanism Updating and Chemical Kinetic Analysis

For spark ignition and compression ignition ammonia engines, a typical approach to ensure stable operation involves the blending of ammonia with hydrogen and diesel, respectively. For the ammonia/hydrogen fuel, in this study a comprehensive comparison was conducted firstly for the differences among existing chemical mechanisms according to the experimental data of ignition, oxidation, and flame propagation. The result indicates that the current reaction mechanisms for ammonia/hydrogen fuel exhibit high prediction accuracy only within limited condition ranges. Subsequently, considering the completeness of combustion reaction pathways for ammonia/hydrogen fuel, a chemical mechanism of ammonia and ammonia/hydrogen fuel was developed and optimized in this study, and the comprehensive validation demonstrates the accuracy of the developed mechanism. On this basis, the ammonia mechanism was integrated with the detailed n-heptane mechanism to derive a mechanism for ammonia/diesel fuel that includes 1351 species and 6227 reactions. The good performance of this mechanism was demonstrated in terms of the experimental data of ignition and oxidation. In addition, the ignition sensitivity and reaction pathways of ammonia/hydrogen fuel were investigated based on the constructed mechanism, and the significance of C3–C7/N reactions was also analyzed for the ammonia/diesel fuel ignition process.

Autoignition of Reacting Hydrocarbon Mixture With Negative Temperature Coefficient Due to the Cold-Spot and Cold Chamber Wall

AbstractAutoignition of an n-heptane/air mixture was simulated in nonuniform temperature environments of a rapid compression machine (RCM) and shock-tube (ST) with and without the presence of a cold-spot. The simulations were performed to investigate how the presence of a cold-spot and the cold boundary layer of the chamber wall may affect the ignition delay of the hydrocarbon mixture with negative temperature coefficient (NTC) behavior. The simulations were performed using three models: (1) three-dimensional (3D) computational fluid dynamics (CFD) model, (2) zero-dimensional (0D) homogenous batch reactor model by including the heat transfer model, and (3) 0D adiabatic homogenous batch reactor model. A detailed n-heptane mechanism was reduced in this work and used for 3D combustion modeling. A cold-spot critical radius of 7 mm was determined, which affects the ignition delay by more than 9%. In addition, two combustion modes were observed in the combustion chamber with a nonuniform temperature environment. With the first combustion mode, combustion starts at the high gas temperature region of the combustion chamber and quickly propagates toward the periphery of the chamber. In this combustion mode, the location of the maximum concentration of hydroxyl radical and the maximum temperature are the same. With the second combustion mode, the combustion starts at the periphery of the chamber, where the temperature is lower than the center of the chamber due to heat transfer to the cold chamber wall. The location of maximum concentration of the hydroxyl radical and maximum temperature is different with this combustion mode. The two observed combustion modes are due to the NTC behavior of the n-heptane mixture. The 0D homogenous batch reactor model (with and without heat transfer models) failed to mimic the ignition delay accurately when the second combustion mode was present. In addition, a propagating combustion has been observed in the simulation which is in agreement with some of the optical autoignition diagnostics of these hydrocarbons. This propagating combustion leads to a gradual pressure rise during autoignition, rather than a sharp pressure rise. The results of this work show that 0D homogenous batch reactor models are unable to simulate autoignition of mixtures with NTC behavior.

Mechanism of Methane Addition Affects the Ignition Process of n-heptane under Dual Fuel Engine-Like Conditions

for saving energy and protecting the environment, natural gas has been widely used in internal combustion engines, which makes the study on the ignition characteristics of natural gas/diesel mixtures important. In this work, the effects of trace methane addition on the ignition delay of n-heptane/air mixtures are numerically studied using a detailed n-heptane mechanism under marine engine-like conditions. The simulations are carried out based on the software CHEMKIN-PRO 18.0 with a closed homogeneous reactor. Results show that the prolonged ignition delay times (IDs) of n-heptane/air mixtures are observed over the whole initial temperature range after methane is added, and the increment of IDs in the negative temperature coefficient (NTC) region is significantly higher than that in high temperature region. The sensitivity analysis indicates that both inhibition and promotion effects of important elementary reactions on n-heptane oxidation are weakened because of methane addition. However, the weakening influence on the promoting effect is more prominent. In addition, the inhibition effect of some elementary reactions that are related to the methane oxidation is enhanced. Thus, the IDs of n-heptane/air mixture are prolonged. The analyses of reaction rate of production (ROP) show that the both the production and consumption rates of key radicals decrease significantly in NTC region after methane is added, but it is negligible in the high temperature region. The study can extend the theoretical basis of ignition characteristics of methane/n-heptane blends under elevated temperatures and pressures.

Applicability of high dimensional model representation correlations for ignition delay times of n-heptane/air mixtures

It is difficult to predict the ignition delay times for fuels with the two-stage ignition tendency because of the existence of the nonlinear negative temperature coefficient (NTC) phenomenon at low temperature regimes. In this paper, the random sampling-high dimensional model representation (RS-HDMR) methods were employed to predict the ignition delay times of n-heptane/air mixtures, which exhibits the NTC phenomenon, over a range of initial conditions. A detailed n-heptane chemical mechanism was used to calculate the fuel ignition delay times in the adiabatic constant-pressure system, and two HDMR correlations, the global correlation and the stepwise correlations, were then constructed. Besides, the ignition delay times predicted by both types of correlations were validated against those calculated using the detailed chemical mechanism. The results showed that both correlations had a satisfactory prediction accuracy in general for the ignition delay times of the n-heptane/air mixtures and the stepwise correlations exhibited a better performance than the global correlation in each subdomain. Therefore, it is concluded that HDMR correlations are capable of predicting the ignition delay times for fuels with two-stage ignition behaviors at low-to-intermediate temperature conditions.

Fuel-rich n-heptane oxidation: A shock tube and laser absorption study

The chemical kinetics of n-heptane (n-C7H16) – an important reference compound for real fuels – oxidation are well studied at stoichiometric and lean conditions. However, there is only limited information on the n-heptane chemical kinetics in fuel-rich combustion. In order to verify the accuracy of chemical kinetic models at these conditions, the oxidation of rich n-heptane mixtures has been investigated. Combustion of n-C7H16/O2/Ar mixtures at equivalence ratios, φ, of 2.0 and 3.0 behind reflected shock waves has been studied at temperatures ranging from 1066 to 1502 K and at pressures ranging from 1.4 to 6.2 atm. Reaction progress was monitored by recording pressure and absorption time-histories of ethylene (C2H4) and n-heptane at a location 2 cm from the endwall of a 14-cm inner diameter shock tube. Ethylene and n-heptane absorption time-histories were measured, respectively, using absorption spectroscopy at 10.532 μm from a tunable CO2 laser and at around 3.4 μm from a continuous wave distributed feedback interband cascade laser (ICL). The measured absorption time-histories were compared with modeled predictions from the Lawrence Livermore National Lab (LLNL) detailed n-heptane reaction mechanism. To the best of our knowledge, current data are the first time-resolved n-heptane and ethylene concentration measurements conducted in a shock tube at these conditions.

A skeletal mechanism modeling on soot emission characteristics for biodiesel surrogates with varying fatty acid methyl esters proportion

A new developed four-component biodiesel combustion skeletal mechanism comprising methyl decenoate, methyl-5-decenoate, n-decane and methyl linoleate is presented in this work, which could predict soot formation trends with varying fatty acid methyl esters proportion. It was established based on a detailed n-heptane mechanism, HACA-mechanism and our previously developed four-component biodiesel combustion skeletal mechanism without soot formation mechanism. This new developed mechanism consists of 134 species and 475 reactions. In order to validate the feasibility of this new skeletal mechanism, ignition delay testing, constant volume combustion chamber experiment testing and diesel engine experiment testing were performed. The result indicates that it is suitable to predict ignition behavior, flame lift-off length, soot shape and distribution, cylinder pressures, heat release rate and NOx emission trends of biodiesel with varying fatty acid methyl esters proportion.

Prediction Accuracy and Efficiency of the n-Heptane Mechanism at Different Reduction Levels

The detailed combustion mechanism can be coupled with the computational fluid dynamics (CFD) software to simulate the combustion process in a practical engine. However, the computing time may be unfeasibly long. To improve the efficiency of the simulations, a reduced mechanism is preferable. However, the combustion characteristics and prediction accuracy will be influenced by the reduction of the combustion mechanism. In this work, the effects of the reduction of the detailed n-heptane mechanism on the prediction accuracy and efficiency were investigated theoretically. The reduction was based on the directed relation graph method without revising the original kinetic parameters. The results indicated that the reduced combustion mechanism at 1/2 size (1/2 mechanism) of the detailed mechanism performed well and the 1/4 mechanism showed some deviation from the experimental data as a result of the removal of some low-temperature reactions. The 1/8 mechanism performed even worse. An ideal combustion mechanism for coupling with CFD simulations should be of the size between that of the 1/2 mechanism and 1/4 mechanism.

First-stage ignition delay in the negative temperature coefficient behavior: Experiment and simulation

The existence of the first-stage ignition delay (FID) negative temperature coefficient (NTC) behavior was confirmed by rapid compression machine experiments using iso-octane and methyl-cyclohexane. The first-stage NTC behavior of iso-octane is observed in the temperature range 757–782K under 20bar and φ=1. For methyl-cyclohexane, the observed first-stage NTC temperature range is 750–785K under 15bar and φ=0.5. In further iso-octane experiments, the FID is found to be sensitive to the O2 concentration and insensitive to the dilution gas and fuel concentrations. The effects of the FID and its NTC behavior on the total ignition delay NTC were analyzed using a detailed n-heptane mechanism. The contributions to the total ignition delay NTC from the reduced second-stage initial temperature, pressure, and less reactive species pool, together with the NTC of FID were discussed quantitatively. For the first-stage NTC behavior, five competing reactions were identified as being important based on sensitivity analysis, reaction pathway analysis, and simplified mechanism method. They are the backward reaction of second O2 addition, RO2 ⇔ alkene+HO2, QOOH ⇔ cyclic-ether+OH, QOOH ⇔ alkene+HO2, and the beta scission reaction of the alkyl radical. Their competition with the low-temperature branching channel finally leads to the first-stage NTC behavior.

Development and Validation of a Reduced Chemical Kinetic Mechanism for Computational Fluid Dynamics Simulations of Natural Gas/Diesel Dual-Fuel Engines

A reduced chemical kinetic mechanism consisting of 141 species and 709 reactions has been constructed to simulate the combustion of both natural gas and diesel fuels in a dual-fuel engine. Natural gas is modeled as a mixture of methane, ethane, and propane, while the diesel fuel is modeled as n-heptane. The new reduced mechanism combines reduced versions of a detailed n-heptane mechanism and a detailed methane through n-pentane mechanism, each of which was reduced using a direct relation graph method. The reduced dual-fuel mechanism is validated against ignition delay computations with full detailed mechanisms, adiabatic homogeneous charge compression ignition simulations with full detailed mechanisms, experimental premixed laminar flame speeds of CH4/O2/He mixtures at 40 and 60 atm, ignition delay and lift-off length from a diesel spray experiment in a constant-volume chamber, and finally against dual-fuel engine experiments using multidimensional computational fluid dynamics simulations. The engine simu...

Numerical investigation on diesel combustion and emissions with a standard combustion model and detailed chemistry

The aim of this study was to determine possibilities of the soot and NOx emissions reduction from an existing heavy-duty compression-ignition (CI) engine based only on in-cylinder techniques. To that end numerical simulations of such processes as a multiphase fuel flow through injector nozzles, a liquid fuel jet breakup and evaporation, combustion and emissions formation were performed in AVL Fire 3D CFD software. The combustion process was calculated with the ECFM-3Z model and with the detailed n-heptane oxidation scheme that consisted of 76 species and 349 reactions. Both approaches of combustion modeling were validated against experimental data from the existing engine working under 75% and 100% loads. As for the reduction of the NOx emission an introduction of exhaust gas recirculation (EGR) was investigated. As for the soot concentration reduction such measures as an increased rail pressure, application of a post-injection and an increased injector nozzles conicity were investigated. Finally the ECFM-3Z model with emissions models, as well as the n-heptane mechanism predicted that it is possible to reach specified emissions limits with application of EGR, post-injection and increased nozzles conicity.

Validation of a Newly Developed n-Heptane Reduced Chemistry and Its Application to Simulations of Ignition Quality Tester, Diesel, and HCCI Combustion

A skeletal mechanism (144 species) and a corresponding reduced mechanism (62 species) were developed on the basis of the most recent detailed n-heptane mechanism by Lawrence Livermore National Laboratories (LLNL, version 3.1, 2012) (Mehl et al., 2011, “Kinetic Modeling of Gasoline Surrogate Components and Mixtures Under Engine Conditions,” Proc. Combust. Inst., 33, pp. 193–200), in order to assess the mechanism's performance under various practical combustion conditions. These simplified mechanisms were constructed and validated under shock tube conditions. Three-dimensional computational fluid dynamics (3D CFD) simulations with both simplified mechanisms were conducted for the following modeling applications: ignition quality tester (IQT), diesel engine, and homogeneous charge compression ignition (HCCI) engine. In comparison with experimental data, the simulation results were found satisfactory under the diesel condition but inaccurate for both the IQT and HCCI conditions. For HCCI, the intake temperature used in the simulation had to be increased 30 K in order to be consistent with the engine data provided by Guo et al. (2010, “An Experimental and Modeling Study of HCCI Combustion Using n-Heptane,” ASME J. Eng. Gas Turbines Power, 132(2), 022801). Exploration of possible causes is conducted leading to the conclusion that refinement in the mechanism is needed for accurate prediction of combustion under IQT and HCCI conditions.

Ozone-Assisted Combustion—Part I: Literature Review and Kinetic Study Using Detailed n-Heptane Kinetic Mechanism

In this first paper, the authors undertake a review of the literature in the field of ozone-assisted combustion in order to summarize literature findings. The use of a detailed n-heptane combustion model including ozone kinetics helps analyze these earlier results and leads into experimentation within the authors' laboratory using a single-cylinder, direct-injection compression ignition engine, briefly discussed here and in more depth in a following paper. The literature and kinetic modeling outcomes indicate that the addition of ozone leads to a decrease in ignition delay, both in comparison to no added ozone and with a decreasing equivalence ratio. This ignition delay decrease as the mixture leans is counter to the traditional increase in ignition delay with decreasing equivalence ratio. Moreover, the inclusion of ozone results in slightly higher temperatures in the cylinder due to ozone decomposition, augmented production of nitrogen oxides, and reduction in particulate matter through radial atomic oxygen chemistry. Of additional importance, acetylene levels decrease but carbon monoxide emissions are found to both increase and decrease as a function of equivalence ratio. This work illustrates that, beyond a certain level of assistance (approximately 20 ppm for the compression ratio of the authors' engine), adding more ozone has a negligible influence on combustion and emissions. This occurs because the introduction of O3 into the intake causes a temperature-limited equilibrium set of reactions via the atomic oxygen radical produced.

Development and Parametric Evaluation of a Tabulated Chemistry Tool for the Simulation of n-Heptane Low-Temperature Oxidation and Autoignition Phenomena

Accurate modelling of preignition chemical phenomena requires a detailed description of the respective low-temperature oxidative reactions. Motivated by the need to simulate a diesel oil spray evaporation device operating in the “stabilized” cool flame regime, a “tabulated chemistry” tool is formulated and evaluated. The tool is constructed by performing a large number of kinetic simulations, using the perfectly stirred reactor assumption. n-Heptane is used as a surrogate fuel for diesel oil and a detailed n-heptane mechanism is utilized. Three independent parameters (temperature, fuel concentration, and residence time) are used, spanning both the low-temperature oxidation and the autoignition regimes. Simulation results for heat release rates, fuel consumption and stable or intermediate species production are used to assess the impact of the independent parameters on the system’s thermochemical behaviour. Results provide the physical and chemical insight needed to evaluate the performance of the tool when incorporated in a CFD code. Multidimensional thermochemical behaviour “maps” are created, demonstrating that cool flame activity is favoured under fuel-rich conditions and that cool flame temperature boundaries are extended with increasing fuel concentration or residence time.

Global reaction mechanism for the auto-ignition of full boiling range gasoline and kerosene fuels

Compact reaction schemes capable of predicting auto-ignition are a prerequisite for the development of strategies to control and optimise homogeneous charge compression ignition (HCCI) engines. In particular for full boiling range fuels exhibiting two stage ignition a tremendous demand exists in the engine development community. The present paper therefore meticulously assesses a previous 7-step reaction scheme developed to predict auto-ignition for four hydrocarbon blends and proposes an important extension of the model constant optimisation procedure, allowing for the model to capture not only ignition delays, but also the evolutions of representative intermediates and heat release rates for a variety of full boiling range fuels. Additionally, an extensive validation of the later evolutions by means of various detailed n-heptane reaction mechanisms from literature has been presented; both for perfectly homogeneous, as well as non-premixed/stratified HCCI conditions. Finally, the models potential to simulate the auto-ignition of various full boiling range fuels is demonstrated by means of experimental shock tube data for six strongly differing fuels, containing e.g. up to 46.7% cyclo-alkanes, 20% napthalenes or complex branched aromatics such as methyl- or ethyl-napthalene. The good predictive capability observed for each of the validation cases as well as the successful parameterisation for each of the six fuels, indicate that the model could, in principle, be applied to any hydrocarbon fuel, providing suitable adjustments to the model parameters are carried out. Combined with the optimisation strategy presented, the model therefore constitutes a major step towards the inclusion of real fuel kinetics into full scale HCCI engine simulations.

Chemical kinetic mechanism and a skeletal model for oxidation of n-heptane/methanol fuel blends

It has been found in previous experimental studies that the ignition of diesel or n-heptane is delayed by methanol addition. However, detailed analysis of the interaction between the two fuels especially under low temperature oxidation has not been reported previously. In order to discover the chemical mechanism and create a skeletal model which can be coupled with 3-D simulation software efficiently, following works were conducted: Firstly, by using a detailed n-heptane oxidation mechanism which was slightly revised, the reaction paths analysis was conducted to seek the coupled relationship between n-heptane and methanol; Secondly, based on the reaction paths and sensitive analysis, a skeletal kinetic model including only 38 reactions related to 30 kinds of species was created to predict the ignition delay and the combustion of methanol/n-heptane blends as well as each pure fuel. The detailed mechanism analysis results show that when two fuels are blended, the radical pool is the only bridge between them. OH· is converted into H2O2 when affected by methanol, and H2O2 then frozen due to its high decomposition activation energy in the temperature below about 1000K, thus the reaction activity of the whole system deceases; The skeletal model test result shows that the ignition delay of the n-heptane, methanol and the blends is well predicted under various equivalence ratios, initial temperatures and pressures compared with the results of experiments or detailed mechanism. HCCI engine test also show that the ignition, in-cylinder temperature as well as the major species all have satisfactory predictions.

Numerical Investigation of Homogeneous Charge Compression Ignition (HCCI) Combustion with Detailed Chemical Kinetics Using On-the-Fly Reduction

An on-the-fly mechanism reduction approach is employed in this paper to integrate detailed chemical kinetics with a computational fluid dynamics (CFD) code. The reduction methodology employs an instantaneous element flux analysis to identify redundant species and reactions for given local conditions. The emphasis of this work is focused on the numerical study of homogeneous charge compression ignition (HCCI) engine combustion in CFD code KIVA-3V using a detailed n-heptane oxidation mechanism with 653 species and 2827 elementary reactions. The proposed on-the-fly reduction method predicts species concentrations, temperatures, and pressures with high fidelity compared to solutions obtained using the detailed mechanism. In the mean time, central processing unit (CPU) time on chemistry calculation is tremendously reduced, enabling integration of complex kinetic mechanisms in engine CFD. When detailed chemistry is combined with realistic flow simulation, accurate predictions of in-cylinder combustion behavior ...

Acceleration of the chemistry solver for modeling DI engine combustion using dynamic adaptive chemistry (DAC) schemes

Acceleration of the chemistry solver for engine combustion is of much interest due to the fact that in practical engine simulations extensive computational time is spent solving the fuel oxidation and emission formation chemistry. A dynamic adaptive chemistry (DAC) scheme based on a directed relation graph error propagation (DRGEP) method has been applied to study homogeneous charge compression ignition (HCCI) engine combustion with detailed chemistry (over 500 species) previously using an R-value-based breadth-first search (RBFS) algorithm, which significantly reduced computational times (by as much as 30-fold). The present paper extends the use of this on-the-fly kinetic mechanism reduction scheme to model combustion in direct-injection (DI) engines. It was found that the DAC scheme becomes less efficient when applied to DI engine simulations using a kinetic mechanism of relatively small size and the accuracy of the original DAC scheme decreases for conventional non-premixed combustion engine. The present study also focuses on determination of search-initiating species, involvement of the NOx chemistry, selection of a proper error tolerance, as well as treatment of the interaction of chemical heat release and the fuel spray. Both the DAC schemes were integrated into the ERC KIVA-3v2 code, and simulations were conducted to compare the two schemes. In general, the present DAC scheme has better efficiency and similar accuracy compared to the previous DAC scheme. The efficiency depends on the size of the chemical kinetics mechanism used and the engine operating conditions. For cases using a small n-heptane kinetic mechanism of 34 species, 30% of the computational time is saved, and 50% for a larger n-heptane kinetic mechanism of 61 species. The paper also demonstrates that by combining the present DAC scheme with an adaptive multi-grid chemistry (AMC) solver, it is feasible to simulate a direct-injection engine using a detailed n-heptane mechanism with 543 species with practical computer time.

Experimental and Numerical Investigation of n-Heptane/Air Counterflow Nonpremixed Flame Structure

An experimental and numerical investigation of prevaporized n-heptane nitrogen-diluted nonpremixed flames is reported. The major objective is to provide well-resolved experimental data regarding the structure and emission characteristics of these flames, including profiles of major species (N 2 , O 2 , C 7 H 16 , CO 2 , CO, H 2 ), hydrocarbon intermediates (CH 4 , C 2 H 4 , C 2 H 2 , C 3 H x ), and soot precursors (C 6 H 6 ). A counterflow flame configuration is employed, because it provides a nearly one-dimensional flat flame that facilitates both the detailed measurements and simulations using comprehensive chemistry and transport models. The measurements are compared with predictions using a detailed n-heptane oxidation mechanism that includes the chemistry of NO, and polycyclic aromatic hydrocarbon formation. The measurements are compared with predictions using a detailed n-heptane oxidation mechanism that includes the chemistry of NO x and polycyclic aromatic hydrocarbon formation. Measurements and predictions exhibit excellent agreement for temperature and major species profiles (N 2 , O 2 , n-C 7 H 16 , CO 2 , CO, and H 2 ), reasonably good agreement for intermediate species (CH 4 , C 2 H 4 , C 2 H 2 , and C 3 H , ), but significant differences with respect to benzene profiles. Consequently, the benzene submechanism was synergistically improved using pathway analysis and measured benzene profiles.

HCCI ENGINE MODELING AND EXPERIMENTAL INVESTIGATIONS—PART 1: THE REDUCTION, COMPOSITION AND VALIDATION OF A n-HEPTANE/ISO-OCTANE MECHANISM

A certain possible approach for the control of HCCI chemistry is to use kinetic chemistry mechanisms. This opens a field of interest that lead to the composition of a validated reduced PRF chemistry mechanism. For this purpose a skeletal chemical reaction mechanism for n-heptane and for iso-octane are constructed from a detailed n-heptane and iso-octane mechanism of the Chalmers University of Technology. Subsequently these two mechanisms are forged into one reduced chemical reaction mechanism for mixtures of n-heptane and iso-octane (39 species and 47 reactions). This mechanism is numerically validated against the Chalmers mechanisms, respecting the HCCI application range. The reduced mechanism is also successfully numerically validated against another more detailed mechanism provided by LLNL. Engine experiments are performed validating this mixture mechanism with respect to the fuel composition containing n-heptane and iso-octane. The influence of the compression ratio and the equivalence ratio is also studied and used to validate the reduced PRF mechanism.

An experimental and numerical investigation of n-heptane/air counterflow partially premixed flames and emission of NO x and PAH species

An experimental and numerical investigation of counterflow prevaporized partially premixed n-heptane flames is reported. The major objective is to provide well-resolved experimental data regarding the detailed structure and emission characteristics of these flames, including profiles of C 1–C 6, and aromatic species (benzene and toluene) that play an important role in soot formation. n-Heptane is considered a surrogate for liquid hydrocarbon fuels used in many propulsion and power generation systems. A counterflow geometry is employed, since it provides a nearly one-dimensional flat flame that facilitates both detailed measurements and simulations using comprehensive chemistry and transport models. The measurements are compared with predictions using a detailed n-heptane oxidation mechanism that includes the chemistry of NO x and PAH formation. The reaction mechanism was synergistically improved using pathway analysis and measured benzene profiles and then used to characterize the effects of partial premixing and strain rate on the flame structure and the production of NO x and soot precursors. Measurements and predictions exhibit excellent agreement for temperature and major species profiles (N 2, O 2, n-C 7H 16, CO 2, CO, H 2), and reasonably good agreement for intermediate (CH 4, C 2H 4, C 2H 2, C 3H x ) and higher hydrocarbon species (C 4H 8, C 4H 6, C 4H 4, C 4H 2, C 5H 10, C 6H 12) and aromatic species (toluene and benzene). Both the measurements and predictions also indicate the existence of two partially premixed regimes; a double flame regime for ϕ < 5.0 , characterized by spatially separated rich premixed and nonpremixed reaction zones, and a merged flame regime for ϕ > 5.0 . The NO x and soot precursor emissions exhibit strong dependence on partial premixing and strain rate in the first regime and relatively weak dependence in the second regime. At higher levels of partial premixing, NO x emission is increased due to increased residence time and higher peak temperature. In contrast, the emissions of acetylene and PAH species are reduced by partial premixing because their peak locations move away from the stagnation plane, resulting in lower residence time, and the increased amount of oxygen in the system drives the reactions to the oxidation pathways. The effects of partial premixing and strain rate on the production of PAH species become progressively stronger as the number of aromatic rings increases.