Laminar Burning Velocities Of Ethanol Research Articles

Effect of ethanol addition on the laminar burning velocities of gasoline surrogates

Laminar burning velocities (LBV) and Markstein lengths of spherical flames of n-heptane (H), iso-octane (O), and ethanol (E) and their binary and ternary mixtures (in equal volume fractions) at elevated pressures and temperatures are experimentally investigated. Measurements are performed in a constant volume combustion vessel using two distinct techniques: flame front imaging and pressure rise rate. For pure components, ethanol shows a higher LBV compared to n-heptane and iso-octane at same conditions. A pressure dependence on LBV of each pure component is observed where ethanol is found to have the strongest pressure dependence. This is also indicated by the higher negative coefficients in three-body termination reactions through a sensitivity analysis. For binary mixtures, the EH mixture was found to have the highest LBVs compared to other blends. The pressure dependence on LBV of ethanol is also present in binary mixtures where at a higher pressures the EO blend is found to have a lower LBV compared to the OH blend due to competing reactions against the H radical pool. Non-linear behaviour of the EH mixture’s LBV was observed and verified through the chemical kinetics suggesting the widely used mixing rules for blends might need additional improvements, especially at higher temperatures. An equal volume EHO ternary mixture shows the LBV to be similar to the OH mixture at 380 K. At 450 K, the LBVs differ by 7% at atmospheric pressure, but due to ethanol’s pressure dependence, this difference decreases to zero as the pressure increases to 4 bar.

Research on ethanol and toluene's synergistic effects on auto-ignition and pressure dependences of flame speed for gasoline surrogates

Spark-assisted compression ignition (SACI) has a promising potential to substantially improve engine's fuel efficiency. To this end, two exothermic stages in SACI combustion, flame propagation and auto-ignition, need to be well organized to increase control authority of bulk ignition timing especially in lean burn. In this study, three gasoline surrogates, namely EPRF, ETPRF and TPRF, formulated through blending ethanol/toluene with primary reference fuel (PRF) and having the same research octane number (RON) and octane sensitivity (S), were used to conduct experiments in a rapid compression machine (RCM) under lean engine-relevant conditions (10–30 bar and 722–862 K). Under different ethanol blending ratios, both ethanol's synergistic effect during auto-ignition and its stronger pressure dependence of flame speed (SFlame) than toluene were observed. The ethanol's synergistic effect is mainly attributed to its more HO2 production and then faster consumption by benzyl which results in more OH radical production. As for the stronger pressure dependence of SFlame of ethanol, at 722 K, it is primarily determined by the stronger pressure dependence of H radical in EPRF's flame structure rather than the promotion effect from critical reactions on SFlame; while at 862 K, these two factors influence the pressure dependence of SFlame simultaneously. Whatever the temperature is, third-body reactions have larger impacts on ethanol's SFlame than on toluene's. In this study, the relative magnitude of SFlame’s pressure dependence between ethanol and toluene shows rationality at lower φ and higher T, which is in line with the pressure exponents extracted from the existing high-p laminar burning velocities of ethanol and toluene. Further verification was made in a spark-ignition engine, which showed that low-carbon alcohols, exhibited stronger pressure dependence of SFlame than monophenyl aromatics in commercial gasoline, represented by toluene. The aforementioned characteristics of ethanol can be utilized under different engine loads and provide a reference in fuel design for lean SACI combustion.

Laminar burning velocity of ethanol premixed combustion enriched with liquefied petroleum gas (LPG)

The laminar burning velocity of ethanol premixed combustion enriched with liquefied petroleum gas (LPG) has been studied experimentally. The study was conducted in a cylindrical combustion chamber, and combustion model was spherically expanding flame. The results showed that the laminar burning velocity of ethanol enriched with 5–10% LPG is higher than that of pure ethanol and that of pure LPG. This is due to the formation of H and OH radicals in the preheating zone, where the reaction occurs to form H2O and release heat. It raises temperature in the preheating zone which contributes to increase in the laminar burning velocity.

The Role of Molecule Clustering by Hydrogen Bond in Hydrous Ethanol on Laminar Burning Velocity

The role of hydrogen bond molecule clustering in laminar burning velocities was observed. The water in hydrous ethanol can change the interaction between water-ethanol molecules. A certain amount of water can become oxygenated which increases the burning velocity. The hydrogen bond interaction pattern of ethanol and water molecules was modeled. Based on the molecular model, azeotropic behavior emerges from ethanol-water hydrogen bond, which is at a 95.1%v composition. The interaction with water molecule causes the ethanol molecule to be clustered with centered oxygenated compound. So, it supplies extra oxygen and provides intermolecular empty spaces that are easily infiltrated by the air. In the azeotropic composition, the molecular bond chain is the shortest, so hypothetically the burning velocity is anticipated to increase. The laminar burning velocity of ethanol fuel was tested in a cylindrical explosion bomb in lean, stoichiometric, and rich mixtures. The experimental result showed that the maximum burning velocity occurred at hydrous ethanol of 95.5%v composition. This discrepancy is the result of the addition of energy from 7.7% free ethanol molecules that are not clustered. At the rich mixture, the burning velocity of this composition is higher than that of anhydrous ethanol.

A laminar burning velocity and flame thickness correlation for ethanol–air mixtures valid at spark-ignition engine conditions

The use of biomass-derived ethanol in spark-ignition engines is an interesting option to decarbonize transport and increase energy security. An engine cycle code valid for this fuel, could help to explore its full potential. Crucial building blocks to model the combustion in ethanol engines are the laminar burning velocity and flame thickness of the ethanol–air–residuals mixture at instantaneous cylinder pressure and temperature. This information is often implemented in engine codes using correlations. A literature survey showed that the few available flame thickness correlations have not yet been validated for ethanol. Also, none of the existing ethanol laminar burning velocity correlations covers the entire temperature, pressure and mixture composition range as encountered in spark-ignition engines. Moreover, most of these correlations are based on measurements that are compromised by the effects of flame stretch and the occurrence of flame instabilities. For this reason, we started working on new correlations based on flame simulations using a one-dimensional chemical kinetics code.In this paper the published experimental data for the laminar burning velocity of ethanol are reviewed. Next, the performance of several reaction mechanisms for the oxidation kinetics of ethanol–air mixtures is compared. The best performing mechanisms are used to calculate the laminar burning velocity and flame thickness of these mixtures in a wide range of temperatures, pressures and compositions. Finally, based on these calculations, correlations for the laminar burning velocity and flame thickness covering the entire operating range of ethanol-fueled spark-ignition engines, are presented. These correlations can now be implemented in an engine code.

Combustion Characteristics of Ethanol and PRF Laminar Flames

In this study, laminar burning velocities of ethanol, iso-octane and n-heptane-air mixtures were determined experimentally over a wide range of equivalence ratio under the various pressures up to 0.5MPa, employing spherically expanding flames. Considering non-linear extrapolations, the effects of stretch was minimized by extrapolating the reference flame speed to vanishing stretch. The laminar burning velocities of iso-octane were found to be lower than those of ethanol and n-heptane throughout the range of experimental equivalence ratios. For all fuels, laminar burning velocities were found to decrease with increase initial pressure. From schlieren images, ethanol, iso-octane and n-heptane-air mixtures on the fuel rich region were found to become unstable at 0.1MPa. For all fuels, increasing initial pressure was found to get flame more unstable and narrow the stable flame region.

The temperature dependence of the laminar burning velocity of ethanol flames

The Heat Flux method was extended for the first time towards liquid fuels and used to determine burning velocities under conditions when the net heat loss from the flame to the burner is zero. Non-stretched flames were stabilized on a perforated plate burner at 1atm. Uncertainties of the measurements were analyzed and assessed experimentally. The overall accuracy of the burning velocities was estimated to be better than ±1cm/s. Excellent reproducibility of the experiments over an extended period of time was demonstrated. Measurements of the adiabatic burning velocity of ethanol+air flames in the range of initial mixture temperatures from 298 to 358K are presented. Experimental results are in a good agreement with the recent literature data obtained in constant volume bombs. Both the ethanol combustion mechanism of Saxena and Williams and the Konnov mechanism significantly over-predict ethanol laminar burning velocities in lean and near-stoichiometric mixtures. The effects of initial temperature on the adiabatic laminar burning velocities of ethanol were interpreted using the correlation SL=SL0 (T/T0)α. Particular attention was paid to the variation of the power exponent α with equivalence ratio at atmospheric pressure. Experimental data and proposed empirical expressions for α as a function of equivalence ratio were summarized. They were compared with the predictions of detailed kinetic models. The existence of a minimum in α in the slightly rich mixtures is demonstrated experimentally and confirmed computationally.

Targeted QSPR for the prediction of the laminar burning velocity of biofuels

The upcoming change from fossil to biorenewable feedstock requires, among others, the identification of new liquid fuels to be used in mobile transportation. Although several molecules similar in structure to current petroleum-based fuels have already been proposed as biofuel candidates, a targeted search should identify molecules which are tailored to the numerous requirements posed by modern combustion engines. Such molecular design approaches strongly depend on reliable predictive models which describe the relation between the fuel's molecular structure and its combustion properties. To this end, we present here a targeted quantitative structure–property relation (TQSPR) for the laminar burning velocity, which is a fundamental indicator for the quality of fuels for spark ignition engines. We present the methodology and demonstrate its feasibility by the correct prediction of the laminar burning velocity of ethanol. We show that the experimental value is predicted well within measurement accuracy for various conditions.

4725 PRFの層流燃焼速度に及ぼすエタノール添加の影響(S56-5 エンジン燃焼-さらなる進化を目指して-(5),S56 エンジン燃焼-さらなる進化を目指して-)

Recently, the environmental issues on an earth scale and the depletion of energy resources are requiring internal combustion engines to improve fuel economy and to reduce NO_x emissions and particles urgently, which cause mainly atmospheric pollution. For this purpose, an alternative fuel and new combustion techniques have been studied so far. In this context, the interest in using alcohols as an engine fuel has increased. Among the various alcohols, Ethanol is known as the most suited fuel for spark-ignition engine. The most attractive features of Ethanol as an SI engine fuel are that Ethanol can be produced from renewable energy sources such as agricultural products and it has high octane number. Ethanol can be used in SI engines as pure or blending with gasoline. For pure Ethanol some modifications on engine design, where it can be used in SI engines by blending with gasoline at low concentrations without any modification. As the combustion properties of Ethanol, however, differ from those of gasoline fuel, it is necessary to investigate the combustion characteristics of Ethanol and the effects of Ethanol addition to gasoline in detail for the proper application of Ethanol to a new internal combustion engine. The main purpose of this work is to measure the laminar burning velocity of Ethanol and clarify the effects of Ethanol addition on octane combustion properties.