Swirl ratio and post injection strategies to improve late cycle diffusion combustion in a light-duty diesel engine

Abstract

Nitrogen oxides (NOx) and soot emissions are the most important pollutants from directinjection diesel engines. In particular, soot formation and oxidation determine the net engine-out soot emissions. These phenomena are complex and competing processes during diesel combustion. Despite many researches implicate the mechanisms of soot formation with soot emissions, the enhancement of the late cycle soot oxidation is the dominant mechanism for a reduction of engine-out soot emissions. The mixing process and the in-cylinder bulk temperature are two important parameters in the development of soot oxidation process. The current research compares different engine strategies to enhance the late cycle mixing controlled combustion process and therefore enhance soot oxidation while maintaining similar gross indicated efficiency in a light-duty engine. For this purpose, a simplified methodology has been used, which analyzes the effect of mixing process and in-cylinder bulk gas temperature on soot oxidation during the late cycle combustion. For carrying out this research, theoretical and experimental tools were used. In particular, the experimental measurements were made in a single-cylinder directinjection light-duty diesel engine varying the swirl ratio and the injection pattern as injection pressure, Start of Energizing (SoE), Energizing Time (ET) and number of injections events. To analyze soot emissions, the combustion luminosity was measured by an optoelectronic probe and the optical thickness parameter (KL) was evaluated by the two-color pyrometry method. The apparent combustion time (ACT-1) was used as mixing time tracer. Results show that an increase in swirl ratio implies an improvement on the mixing process and higher values of average bulk temperature during the late-cycle diffusion combustion. Both phenomena produce an enhancement in the soot oxidation process. In the lowest swirl ratio case, a suitable injection strategy based on multiple injections, provides similar results of soot oxidation process (and therefore, the emissions) as high swirl ratio case.

Influence of aging of a diesel injector on multiple injection strategies

“…As a result, the amount of fuel burned in the premixed phase is reduced, which leads to a reduction in the combustion peak temperature [2], determinant for the formation of NO x [5,6]. Regarding post injection strategies, literature work widely refers to this technique as a tool for the reduction of soot exhaust emissions [7,8]. Specifically, a post injection introduces momentum in the latter phase of combustion, which also enhances mixing within the cylinder bowl and the oxidation of soot formed by the main injection [9,10].…”

Effects of rail pressure control on fuel consumption, emissions and combustion parameters in a turbocharged diesel engine

“…The application of multiple injection or boot injection strategies offers extended possibilities for the optimization of different parameters. In Benajes, Martín, García, Villalta, & Warey (2017), the enhancement of soot oxidation at the end of the diffusive phase of the combustion was obtained with a proper management of the injection pattern. In Mohan, Yang, Yu, Tay, & Chou (2015), boot injection allowed to reduce NO X emissions, while increasing its duration led to benefits also for soot emissions.…”

Effects of multiple injections on combustion and emissions in a heavy-duty diesel engine at high load and low speed

“…11 A new concept of variable injection pressure of multiple injections was proposed by Poorghasemi et al, 12 and it was found that increasing post injection pressure can reduce the soot emission significantly while the NO emission is in control. Double and single Wiebe function for multiple injection mode diesel engine combustion modeling was developed and validated by Maroteaux et al 13 Benajes et al 14 found that in the lowest swirl ratio case, a suitable injection strategy based on multiple injections provides similar results of soot oxidation process (and therefore, the emissions) as high swirl ratio case.…”