No abstract

No abstract

Experimental data obtained in this study (Part II) complement the speciation data presented in Part I, but also offer a basis for extensive facility cross-comparisons for both experimental ignition delay time (IDT) and laminar flame speed (LFS) observables.To improve understanding of the ignition characteristics of propene, a series IDT experiments were performed in six different shock tubes and two rapid compression machines (RCMs) under conditions not previously studied. This study is the first of its kind to directly compare ignition in several different shock tubes over a wide range of conditions. For common nominal reaction conditions among these facilities, cross-comparison of shock tube IDTs suggests 20-30% reproducibility (2σ) for the IDT observable. The combination of shock tube and RCM data greatly expands the data available for validation of propene oxidation models to higher pressures (2-40 atm) and lower temperatures (750-1750 K).Propene flames were studied at pressures from 1-20 atm and unburned gas temperatures of 295-398 K for a range of equivalence ratios and dilutions in different facilities. The present propene-air LFS results at 1 atm were also compared to LFS measurements from the literature. With respect to initial reaction conditions, the present experimental LFS cross-comparison is not as comprehensive as the IDT comparison; however, it still suggests reproducibility limits for the LFS observable. For the LFS results, there was agreement between certain data sets and for certain equivalence ratios (mostly in the lean region), but the remaining discrepancies highlight the need to reduce uncertainties in laminar flame speed experiments amongst different groups and different methods. Moreover, this is the first study to investigate the burning rate characteristics of propene at elevated pressures (> 5 atm).IDT and LFS measurements are compared to predictions of the chemical kinetic mechanism presented in Part I and good agreement is observed.

The adiabatic laminar burning velocities of a commercial gasoline and of a model fuel (n-heptane, iso-octane, and toluene mixture) of close research octane number have been measured at 358 K. Non-stretched flames were stabilized on a perforated plate burner at 1 atm. The heat flux method was used to determine burning velocities under conditions for which the net heat loss of the flame is zero. Very similar values of flame velocities have been obtained for the commercial gasoline and for the proposed model fuel. The influence of ethanol as an oxygenated additive has been investigated for these two fuels and has been found to be negligible for values up to 15% (vol). Measurements were also performed for ethanol and the three pure components of the model fuel at 298, 358 and 398 K. The results obtained for the studied mixtures, and for pure n-heptane, iso-octane, toluene and ethanol, have been satisfactorily simulated using a detailed kinetic mechanism.

Understanding the combustion chemistry of the butene isomers is a prerequisite for a comprehensive description of the chemistry of C1 to C4 hydrocarbon and oxygenated fuels such as butanol. For the development and validation of combustion models, it is thus crucial to improve the knowledge about the C4 combustion chemistry in detail. Premixed low-pressure (40 mbar) flat argon-diluted (25%) flames of the three butene isomers (1-butene, trans-2-butene and i-butene) were studied under fuel-rich (=1.7) conditions using a newly developed analytical combination of high-resolution in-situ molecular-beam mass 2 spectrometry (MBMS) and in-situ gas chromatography (GC). The time-of-flight MBMS with its high mass resolution enables the detection of both stable and reactive species, while the gas chromatograph permits the separation of isomers from the same sampling volume. The isomer-specific species information and the quantitative mole fraction profiles of more than 30 stable and radical species measured for each fuel were used to extend and validate the C4 subset of a comprehensive flame simulation model. The experimental data shows different destruction pathways for the butene isomers, as expected, and the model is well capable to predict the different combustion behavior of the isomeric flames. The detailed analysis of the reaction pathways in the flame and the respective model predictions are discussed.

No abstract

-Removing the biomass limit is one of the great challenges to further enlarge the share of renewable ethanol as alternative for fossil fuels. One of the possible solutions for this constraint are the ternary GEM (Gasoline-Ethanol-Methanol) blends. The air-to-fuel ratio of these blends is hereby chosen at the value of an E85-blend (9.75 kg air/ kg fuel) while the ethanol is replaced by methanol/gasoline and therefore these blends are called 'isostoichiometric'. If the methanol is produced out of renewable sources, these blends can help extend the part of clean fuels on the market. The ternary blends show few differences in physical properties for the total range of possible blends and are considered as drop-in alternatives to the original E85-blend for a flex fuel engine. In this paper the performance and engine-out emissions of four of these GEM-blends were examined on a 4 cylinder 1.8 l PFI production engine. A single cylinder engine with high compression ratio was used for a preliminary study of the knock behavior of these blends. The measurement results are compared with those on neat gasoline, methanol and ethanol to demonstrate the potential of these ternary blends as a fossil fuel alternative. All the GEM fuels which were tested gave very similar results to E85 and can therefore indeed be used as 'drop-in' fuels for flex-fuel vehicles.

This paper presents new experimental measurements of the laminar flame velocity of components of natural gas, methane, ethane, propane, and n-butane as well as of binary and tertiary mixtures of these compounds proposed as surrogates for natural gas. These measurements have been performed by the heat flux method using a newly built flat flame adiabatic burner at atmospheric pressure. The composition of the investigated air/hydrocarbon mixtures covers a wide range of equivalence ratios, from 0.6 to 2.1, for which it is possible to sufficiently stabilize the flame. Other measurements involving the enrichment of methane by hydrogen (up to 68%) and the enrichment of air by oxygen (oxycombustion techniques) were also performed. Both empirical correlations and a detailed chemical mechanism have been proposed, the predictions being satisfactorily compared with the newly obtained experimental data under a wide range of conditions.