The use of micro-orifice nozzles and swirl in a small HSDI engine operating at a late split-injection LTC regime

Abstract

This paper describes the investigation of low-temperature combustion (LTC) in a small single-cylinder research high-speed direct injection (HSDI) diesel engine. This engine is representative of passenger car turbocharged diesel engines equipped with a particulate trap and an oxidation catalyst. A medium-load operation mode has been evaluated where the diesel fuel is injected in two injection events close to top dead centre, and high levels of exhaust gas recirculation are used (near stoichiometric air-fuel ratios). The combustion is characterized by extremely low emission of nitrogen oxides (of the order of 10–15 parts per million) and low combustion noise. Three injector nozzles have been tested with 6, 12, and 18 orifices. The orifice diameters are in the range 70–120 μM and have been chosen to obtain injector nozzles with the same hydraulic flow. All three nozzles have been tested at a condition without swirl and at a mean swirl number of 1.7. The effects of the nozzle orifice number and swirl have been investigated by means of analysis of fuel spray, combustion, and emissions. It was found that when the number of orifices is increased, the rate of heat release during the first half of combustion is enhanced. However, during the second part of the combustion, interactions between sprays worsen the air-fuel mixing process and reduce the rate of heat release. Swirl was found to amplify the effects of spray interactions. While normally swirl speeds up the combustion in the second half of the combustion, the opposite happens when spray-spray interaction occurs.

Experimental investigation on the effect of injector hole number on engine performance and particle number emissions in a light-duty diesel engine

“…The pressure profile and heat release rate trend can be attributed to better atomization characteristics of injectors with more number of holes with smaller diameter. 4 Figure 3 shows the combustion phases in terms of CA10–CA90 (CA10 corresponding to the start of combustion and CA90 corresponding to the end of combustion) for all three cases. The start of fuel injection timing for all the analyses in this study has been taken as the crank angle corresponding to the start of first pilot injection.…”

“…6,18,19 It has also been reported that a very high hole number results in flame-flame interference among sprays from neighboring holes. 4,20 In recent past, many researchers have shifted their focus toward optical engine as it is an extraordinary tool for in-detail comprehension of the combustion process and visualization of combustion propagation which cannot be obtained from metal engines. [21][22][23][24] Researchers have utilized this technique and also other ultrafast X-ray techniques to develop a better understanding of spray visualization, injection strategies, and combustion processes.…”

Investigation of Cluster-Nozzle Concepts for Direct Injection Diesel Engines

“…Benajes et al [82] have tested an engine with equispaced nozzles with 6, 12 and 18 orifices with and without swirling in-cylinder flow (for brevity denoted swirl). Without swirl, the nozzle with 12 orifices leads to the lowest emission.…”

An experimental study on flat-wall-impinging spray of microhole nozzles under ultra-high injection pressures

“…In addition, the increased injection pressures usually shorten the time required for the droplet vaporization and combustible mixture preparation and then reduce the ignition delay [5]. At the same time, in various published experimental results, it has been shown that the diesel engine emissions are reduced significantly by decreasing the nozzle hole diameter [6][7][8][9]. In small-bore high-speed DI diesel engines, information on the spray-wall interactions is essential to understand the detailed mechanism and to verify the spray and combustion models in engine simulations.…”

“…0.10 mm) and normal injection pressures (P inj , 200 MPa). At the same time, a few researchers used microhole nozzles and ultra-high injection pressures mainly to focus on the combustion process, exhaust emissions, and engine output performance [1,7,8]. In current archives, there are few fundamental experimental data, which are needed for successful engine design and modelling, about the spray and mixture characteristics with the microhole nozzle and ultra-high *Corresponding author: Department of Mechanical System Engineering, University of Hiroshima, 1-4-1 Kagamiyama, Higashi-Hiroshima, 739-8527, Japan.…”