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The combustion chemistry of allene and propyne is critical for the breakdown of higher hydrocarbon fuels and for molecular growth processes. Allene and propyne consumption reactions are primary sources of the key propargyl and allyl radicals, which are closely linked to benzene, polyaromatic hydrocarbons (PAHs), and soot formation paths. However, uncertainties exist concerning aspects of the C3H4 isomers’ chemistry. The article is part of an on-going effort aiming towards the optimization of a comprehensive kinetic mechanism for the high temperature combustion of small (C1–C6) hydrocarbon species. The mechanism is here validated against species data from stoichiometric and fuel-rich laminar premixed allene and propyne flames with considerable success. A critical evaluation of C3H4 consumption pathways has been carried out and the dynamics of benzene formation and destruction are discussed.

The general performance of a porous inert media burner system in terms of radiative efficiency, fuel flexibility, pollutant formation and reliability was determined experimentally. The porous burner of choice has been previously proven of being capable to operate on conventional and alternative gaseous fuels. The present study examines its operation with virtual blends of model fuels in order to assign and evaluate synergistic effects. In this regard, the present work examines mixtures of CH 4 , CO, H 2 and CO 2 on a two-layer burner with a 10 ppi (pores per inch) SiSiC foam flame zone. The study focused on gaseous and solid phase temperature levels and pollutant formation trends over various nominal thermal loads in the lean combustion regime. The burner optimum operating range was identified and results revealed low NO x levels. For a given stoichiometry, the burner is characterized by a NO x level threshold systematically below 20 ppm, independently of the fuel, with however, distinct behaviour especially with respect to CO 2 content. The opposing effects of CO and H 2 addition on CH 4 /air combustion, aside the influence of CO 2 dilution, were assessed on burner operation and radiation efficiency. The CO 2 addition increased measured CO emission levels and decreased the radiation efficiency of the burner. This may also be attributed to the lower adiabatic flame temperature and burning velocity of CO 2 enriched blends, as also acknowledged by supportive numerical calculations. The relative impact of thermal load on temperature, emissions and burner radiation efficiency with respect to equivalence ratio was also studied. It was identified that the specific burner design, delivers wide power flexibility at lean combustion regimes, providing, at the same time, low total pollutant emissions, i.e . less than 50 ppm and high radiation efficiency, i.e. up to 70% for low thermal loads and depending on the stoichiometry.

The work investigates the effect of various post-injection strategies on the flame patterns in a Ricardo Hydra optical single-cylinder, light-duty diesel engine, operated in a partially premixed combustion mode, under low load (IMEP: ca. 2.3 bar), low speed (1200 rpm) conditions. The effect of post-injection fuel amount (12% and 24% of the total fuel quantity per cycle) and post-injection timing (0, 5, 10 deg aTDC) are investigated via pressure trace analysis and optical measurements. Flame propagation is captured by means of high-speed flame natural luminosity imaging and of CH*, C2*, and OH* line-of-sight chemiluminescence measurements. Results suggest that post-injections suppress mixture reactivity but enhance oxidation, and that a larger amount of fuel and/or later post-injection, leads to higher levels of natural luminosity, indicating possible higher soot-out emissions, while post-injection close to the main combustion event appears to have a beneficial effect on the soot oxidation processes.