Joachim Beeckmann

Triple-injection strategy for model-based control of premixed charge compression ignition diesel engine combustion:

Low-temperature combustion concepts are of great interest due to their potential to reduce nitrogen oxides (NOx) and soot simultaneously. However, low-temperature combustion often leads to an increase in total unburnt hydrocarbons and carbon monoxide. Furthermore, combustion sound level becomes a challenge, especially at higher loads. Various studies show that these drawbacks can be compensated by advanced injection strategies, for example, split injections. In this study, a significantly modified triple-injection approach is proposed. First, the corresponding impact on engine performance is evaluated at stationary conditions, and second, its observed advantages are evaluated at transient operation. Stationary results show that NOx, soot, and combustion sound level are simultaneously reduced without losses in fuel efficiency and without any remarkable rise in total unburnt hydrocarbon as well as carbon monoxide emissions, satisfying Euro 6 emission regulations. Under transient conditions, model-based predictive control of the engine, which allows for reliable steady-state measurements and permits validation tests at transient operating points, is successfully demonstrated for single and triple injection. With both injection strategies, control of indicated mean effective pressure, combustion phasing (CA50 (crank angle (CA) when 50% fuel is consumed)), and NOx emissions is achieved. As a result of this work, the identified optimal triple-injection strategy leads to lower total unburnt hydrocarbon emissions and to significantly reduced combustion sound level at the same level for NOx emissions in comparison with the single-injection approach. Thus, the proposed triple-injection strategy combined with sophisticated model-based control is a promising concept for future engine emission control.

Evaluation of partially premixed turbulent flame stability from mixture fraction statistics in a slot burner

Partially premixed combustion is characterized by mixture fraction inhomogeneity upstream of the reaction zone and occurs in many applied combustion systems. The temporal and spatial fluctuations o...

Spray Phenomena of Surrogate Fuels and Oxygenated Blends in a High Pressure Chamber

In this study, we investigate oxygenated blends and Diesel surrogate fuels under engine-like conditions in a high-pressure chamber. The investigated surrogate fuels are composed of n-decane and alpha-methylnaphthalene with different compositions according to the reference cetane numbers (CN) 53, 45, 38 and 23. In addition to the two-component surrogate fuel mixtures, we examine a three-component mixtures composed of n-decane, alpha-methylnaphthalene, and di-n-butyl ether with a reference cetane number of 53 to highlight the influence of adding di-n-butyl ether to the surrogate fuel at constant cetane number. Further, four blends with DNBE contents of 0, 10, 20 and 100 % in EN590 Diesel and corresponding cetane numbers of 53, 57.7, 62.4, and 100 were studied. We examine fuel spray characteristics in the liquid and vapor phases and the relationship between ignition quality and lift-off length. Vapor pressure is observed to significantly affect spray characteristics in the liquid phase. Vapor penetration lengths of the different fuels with the same injection pressure are found to be similar, because the differences of fuel density and viscosity in the vapor phase are too small to considerably affect the momentum flux. However, changing the injection pressures affects the vapor penetration lengths. Results show that CN is a good indicator for ignition delay. Furthermore, we discuss the fuel overlap number (OL) to indicate the separation between the liquid spray core and the reaction zone in engine-like conditions. It is found for the surrogate mixtures that OL generally increases with decreasing CN, while for the DNBE/Diesel mixtures, the opposite trend is observed. The OL number is found to be caused by a combination of cetane number and vapor pressure effects, where CN has the stronger effect for the surrogate mixtures, while the vapor pressure effect is dominant for the DNBE/Diesel blends. In the latter case, the high vapor pressure leads to short liquid penetration length and thereby larger OL number.