Towards identifying flame patterns in multiple, late injection schemes on a single cylinder optical diesel engine

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 (PPC), under low load (IMEP: ca. 2.3 bar) low speed (1200 rpm) conditions. The effect of postinjection 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 indicate that post-injections suppress mixture reactivity but enhances 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

Analysis of CH2_{2}O x OH as marker for fuel-rich air to pure oxy-fuel flames under higher preheat temperature and elevated pressure

The scope of the present work is a numerical and experimental investigation about the range of validity in terms of applicability of CH$_{2}$OxOH as a marker for the heat release rate (HRR) for fuel-rich air to pure oxy-fuel flames including preheating and elevated pressure. Therefore, laminar, freely propagating 1d CH$_{4}$ flames were calculated, where oxygen content in the oxidizer (from air to pure oxy-fuel combustion), inlet temperature and pressure were varied for a wide range of the equivalence ratios. The preheat temperature and pressure were parametrically changed from 300 K to 573 K and 1 bar to 5 bar, respectively. Different reaction mechanisms were used, namely GRI30, DLR, USC/II, Caltech2.3 and ABF. The performance of the CH$_{2}$OxOH as a marker for HRR is assessed in terms of correlation coefficients of their profiles in laminar flames. The comparison of the obtained correlations of CH$_{4}$/air and CH$_{4}$/O$_{2}$ flames shows that in case of air combustion, the HRR can be accurately estimated by the product of CH$_{2}$OxOH for slightly rich flames (Φ = 1.5), whereas the quality of the correlation degrades with increasing equivalence ratio. In contrary, the correlation coefficient increases with higher equivalence ratios in the fuel-rich domain for enhanced oxygen contents in the oxidizer. For pure oxyfuel combustion, the best correlation is found at an equivalence ratio of approximately Φ = 3.0. Elevated pressure leads in all flames to better correlations at lower equivalence ratios compared to standard inlet conditions, whereas preheating induces the opposite trend and expands the valid regime. A series of CH$_{4}$/air flames were also investigated experimentally in a range of the equivalence ratio between 1 < Φ < 2 at standard inlet conditions. The qualitative CH$_{2}$O (excitation at 355 nm) and OH (excitation at 283 nm) concentration were resolved applying two-dimensional LIF for flames stabilized at a McKenna burner. Comparisons show similar trends for measurements and numerical simulations

A comparative study on the effect of simulated EGR environment on spray characteristics under engine-like conditions

Abstract Increasing concern over air quality and security of energy supply poses challenges to engine research and manufacturing. Despite improvements in conventional engine design, many alternatives are winning their place in order to further reduce engine-out emissions. Sophisticated operating modes, such as homogeneous charge compression ignition (HCCI) and Partially premixed Charge Compression Ignition (PCCI), often coupled with exhaust gas recirculation and/or aftertreatment are employed for regulating nitric oxide (NO x ) and soot emission levels. However, a totally homogeneous mixture is unachievable in practical engines. Inherent inhomogeneities in fuel concentration and temperature may significantly affect the ignition and combustion processes, hence various control strategies attract research interest. The present work demonstrates the potential of emission reduction in Diesel engines operating under high boost conditions through a combination of multi-injection strategies and high EGR schemes