Global extinction strain rate experiments of single large hydrocarbon fuels

Includes bibliographical references.An experimental validation study of the flame extinction characteristics of large hydrocarbon fuels is carried out. A counterflow flame burner combined with a liquid fuel vaporization system is utilized at a reduced pressure of 0.84 atm to measure the diffusion flame global extinction strain rate of liquid fuels as a function of fuel dilution. A numerical study is also employed using CHEMKIN to calculate the global extinction strain rate of hydrocarbon fuels, including n-heptane, n-decane, and toluene. Flame extinction measurements of the blended fuels are compared to global flame extinction predictions using a previously published radical index methodology

CFD model for an automobile refueling system

Department of Mechanical Engineering, Colorado State University.Honda R&D Americas, Inc.Testing procedures for automobile refueling systems can be costly. To reduce the amount of testing during the design of refueling systems, car manufacturers desire a CFD tool predictive of system performance. The potential of such a method is demonstrated here

Pre-vaporized ignition behavior of ethyl- and propyl-terminated oxymethylene ethers

Oxymethylene ethers (OMEs) have been studied in recent years for use as compression ignition fuel blendstocks, but the methyl-terminated OMEs commonly studied exhibit properties that are poorly optimized for engine use and distribution. Recent work has shown that OMEs with larger (ethyl, propyl, or butyl) end groups may have superior properties for fuel usage/storage. In this work, we consider ignition of four OMEs - diethoxymethane (E-1-E), dipropoxymethane (P-1-P), ethoxy-(methoxy)2-ethane (E-2-E), and diisopropoxymethane (iP-1-iP) - as representatives of the possible effects of changes to OME structures. To our knowledge, ignition behaviors of the latter three fuels have not been studied prior to this work. We find that all of the tested linear OMEs (E-1-E, P-1-P, and E-2-E) show two-stage ignition at low temperatures and nonlinear ignition behavior, consistent with literature on methyl-terminated OMEs and E-1-E. The nonlinear, branched OME (iP-1-iP) required higher pressure and temperature to ignite than the linear OMEs; further, this fuel experienced only single stage ignition and a linear ignition delay curve. By analogy to existing kinetic mechanisms for ethers and higher alcohols, the chemical basis for the observed trends are hypothesized. Faster ignition of E-2-E results from the additional oxymethylene group providing additional sites for ROO formation and more possible QOOH structures. Slower low temperature ignition of P-1-P is driven by lower H abstraction rates in comparison to E-1-E, however at high temperatures P-1-P ignites faster, driven by increasing abstraction from the additional H site on the propyl group that opens up additional QOOH formation pathways. iP-1-iP ignition is slowed significantly by preferential H abstraction from the central carbon of the isopropyl group, which is crowded and unlikely to bond with O2, however at high temperatures, abstraction from H sites on the methyl groups allows for the ROO cascade initiation and subsequent rapid ignition

A study of ignition and combustion of liquid hydrocarbon droplets in premixed fuel/air mixtures in a rapid compression machine

The combustion of two fuels with disparate reactivity such as natural gas and diesel in internal combustion engines has been demonstrated as a means to increase efficiency, reduce fuel costs and reduce pollutant formation in comparison to traditional diesel or spark-ignited engines. However, dual fuel engines are constrained by the onset of uncontrolled fast combustion (i.e., engine knock) as well as incomplete combustion, which can result in high unburned hydrocarbon emissions. To study the fundamental combustion processes of ignition and flame propagation in dual fuel engines, a new method has been developed to inject single isolated liquid hydrocarbon droplets into premixed methane/air mixtures at elevated temperatures and pressures. An opposed-piston rapid compression machine was used in combination with a newly developed piezoelectric droplet injection system that is capable of injecting single liquid hydrocarbon droplets along the stagnation plane of the combustion chamber. A high-speed Schlieren optical system was used for imaging the combustion process in the chamber. Experiments were conducted by injecting diesel droplet of various diameters (50 µm \u3c do \u3c 400 µm), into methane/air mixtures with varying equivalence ratios (0 \u3c ϕ \u3c 1.2) over a range of compressed temperatures (700 K \u3c Tc \u3c 940 K). Multiple autoignition modes was observed in the vicinity of the liquid droplets, which were followed by transition to propagating premixed flames. A computational model was developed with CONVERGE™, which uses a 141 species dual-fuel chemical kinetic mechanism for the gas phase along with a transient, analytical droplet evaporation model to define the boundary conditions at the droplet surface. The simulations capture each of the different ignition modes in the vicinity of the injected spherical diesel droplet, along with bifurcation of the ignition event into a propagating, premixed methane/air flame and a stationary diesel/air diffusion flame

Physiochemical Property Characterization of Hydrous and Anhydrous Ethanol Blended Gasoline

Water removal during the production of bioethanol is highly energy intensive. At the azeotropic point, the mixture can no longer be separated via fractional distillation, so expensive and energy intensive methods are required for further purification. Hence, there is an interest in using hydrous ethanol at the azeotropic point to improve the energy balance of ethanol fuel production. Currently there is a lack of available thermophysical property data for hydrous ethanol gasoline fuel blends. These data are important to understand the effect of water on critical fuel properties and to evaluate the potential of using hydrous ethanol fuels in conventional and optimized spark ignition engines. In this study, gasoline was blended with 10, 15, and 30 vol % of anhydrous and hydrous ethanol. The distillation curve, Reid vapor pressure, vapor lock protection potential, viscosity, density, haze and phase separation points, and lower heating value were measured for each blend, and the results were compared to ASTM D4814, the standard specification for automotive spark ignition engine fuels. The majority of the properties measured for the low- and midlevel hydrous ethanol blends are not significantly different from those of the corresponding anhydrous ethanol blends. The only differences observed between the hydrous and anhydrous fuels were in their viscosity and phase separation. The viscosity increased as the total water content increased, whereas the phase separation temperatures decreased with an increasing hydrous ethanol fraction. The results of this study suggest that hydrous ethanol blends may have the potential to be used in current internal combustion engines as a drop-in fuel and in future engine designs tuned to operate on fuels with high levels of ethanol

Poly(oxymethylene) Ethers: Alternative Diesel Fuels with Low Sooting Tendencies

Presentation given at the 2022 ACS Fall Meeting in Chicago IL on August 25 2022. Soot has been identified as the second-largest source of climate change after CO2 and it contributes to ambient fine particulates that cause millions of deaths worldwide each year. Diesel engines contribute significantly to total soot emissions because diesel fuels have high sooting tendencies. Poly(oxymethylene) ethers (POMEs) are alternative diesel fuels that can be produced from waste CO2 with low soot emissions. The structures of the POMEs in these earlier studies are alternating oxygen and carbon atoms terminated with methyl groups on both ends. Unfortunately, these methyl-POMEs suffer from high water solubility and low energy density. Replacing the methyl groups with larger alkyl groups can overcome these disadvantages, but at the cost of higher sooting tendencies. To optimize this trade-off, the sooting tendencies of methyl-POMEs and alkyl-POMEs need to be quantified. In this work, a series of methyl-POMEs and alkyl-POMEs were synthesized and their sooting tendencies were quantified. The test compounds contained a wide range of terminating groups (methyl, ethyl, propyl, iso-propyl, butyl, iso-butyl, sec-butyl, iso-pentyl, and tetrahydrofurfuryl), cases where the terminating groups were identical at the two ends and where they differed, and from one to five oxymethylene units. The sooting tendencies were characterized by the Yield Sooting Index (YSI), which is based on the maximum soot concentration measured in coflow diffusion flames whose fuel is CH4 doped with 1000 ppm or 3000 ppm of each test compound. The YSIs of the POMEs vary significantly with fuel structure, but in all cases are at least one order of magnitude lower than a certification diesel fuel. We proposed some decomposition pathways that justified the difference among the YSIs. The lower heating value (LHV) was also measured to evaluate the energy penalty of the oxygen atoms. The calculated YSI/LHV of the POMEs are lower than conventional diesel fuels and their components. </p