**2. Experimental apparatus**

### **2.1 UMH nozzle structure**

Figure 1 shows the schematic of the UMH nozzle (Miao et al.,2009). It consists of a needle and a body, and has the following characteristics: (1) there are two layers of injection holes

Experimental Investigation on Premixed Combustion in a Diesel Engine with Ultra-Multihole Nozzle 55

Figure 2 shows the schematic comparison between the existing conventional nozzle and the UMH nozzle. There is only one layer of holes on the conventional nozzle, so sprays possibly impinge on the wall of the combustion chamber or the cylinder liner to cause high HC and CO emissions. Sprays might impinge at point A as shown in Figure 2(a). The UMH nozzle, however, has two layers of holes and the cone angle of the under-layer injection holes is larger than that of the upper-layer holes. Two sprays of upper and under-layer meet in the space of the combustion chamber, for example, at point B as shown in Figure 2(b). The results showed that the UMH nozzle exhibits shorter spray penetration than does the conventional nozzle (Miao et al.,2009). This not only avoids fuel sprays impingement on the wall of the combustion chamber or the cylinder liner, but also strengthens sprays turbulence, which promotes fuel-air mixing. Therefore, the result is a more homogeneous

Type Hole number Hole diameter (mm) Flow rate (l/min)@10MPa

Table 1 lists the specifications of test nozzles. It can be seen that the flow rate of the UMH nozzle with smaller diameter hole is higher than that of the original nozzle by up to 67%, which helps the UMH nozzle not only shorten the injection duration and also improve fuel

The specifications of the test engine are shown in Table 2. Its operating conditions are set at 1400 r/min, 0.575MPa and 1000 r/min, 0.279MPa. The test engine is operated on the commercially available diesel fuel with the cetane number of 51 in all the test cases. The coolant temperature is set to 80±3°C. Figure 3 gives the combustion experimental apparatus. The EGR cooler and the intercooler are water-cooled, with water circulation volume and water temperature that are adjustable. The inlet air temperature after the intercooler is maintained at 40±3°C during the whole experiment. The fuel injection is performed by a high-pressure common-rail electric-controlled system on the engine. The exhaust gas emissions are measured using a HORIBA MEXA-7100 gas analyzer, smoke density (soot) measured using an AVL 415s smoke meter, and particle matter (PM) measured using an AVL 472 partial-flow particulate sampler which allows double particulate filters to be

exposed. In-cylinder pressure is acquired using a KISTLER cylinder pressure sensor.

Cylinder number-bore×stroke(mm) 6-110×115 Rated power/speed(kW /r/min) 155/2300 Maximum torque/speed(N.m/r/min) 680/1400 Minimum torque/speed(N.m/r/min) 580~620/1000 Minimum BSFC\*(g/kW.h) 205

Model CA6DF2

Type In-line, supercharged, inter-cooled

mixture required to perform the premixed combustion in diesel engines.

Table 1. Specifications of test nozzles

**2.2 Combustion experimental apparatus** 

atomization.

Original nozzle 8 0.17 1.2 UMH nozzle 16 0.16 2

in the front part of body. Any injection hole of upper layer and the corresponding injection hole of under layer are positioned in a vertical plane; (2) the injection holes cone angle (here defined as the angle of cone consisting of all the axes of injection holes on the same layer) of the under-layer holes is larger than that of the upper-layer holes(α2>α1); and (3) it has a large enough flow area of holes such that cyclic fuel can be completely injected into the combustion chamber prior to ignition, which is a prerequisite for premixed combustion.

Fig. 1. Schematic of UMH nozzle

Fig. 2. Schematic comparison between the conventional and UMH nozzle (a) Conventional nozzle (b) UMH injection nozzle

Figure 2 shows the schematic comparison between the existing conventional nozzle and the UMH nozzle. There is only one layer of holes on the conventional nozzle, so sprays possibly impinge on the wall of the combustion chamber or the cylinder liner to cause high HC and CO emissions. Sprays might impinge at point A as shown in Figure 2(a). The UMH nozzle, however, has two layers of holes and the cone angle of the under-layer injection holes is larger than that of the upper-layer holes. Two sprays of upper and under-layer meet in the space of the combustion chamber, for example, at point B as shown in Figure 2(b). The results showed that the UMH nozzle exhibits shorter spray penetration than does the conventional nozzle (Miao et al.,2009). This not only avoids fuel sprays impingement on the wall of the combustion chamber or the cylinder liner, but also strengthens sprays turbulence, which promotes fuel-air mixing. Therefore, the result is a more homogeneous mixture required to perform the premixed combustion in diesel engines.


Table 1. Specifications of test nozzles

54 Fuel Injection in Automotive Engineering

in the front part of body. Any injection hole of upper layer and the corresponding injection hole of under layer are positioned in a vertical plane; (2) the injection holes cone angle (here defined as the angle of cone consisting of all the axes of injection holes on the same layer) of the under-layer holes is larger than that of the upper-layer holes(α2>α1); and (3) it has a large enough flow area of holes such that cyclic fuel can be completely injected into the combustion chamber prior to ignition, which is a prerequisite for premixed combustion.

> needle body

Fig. 1. Schematic of UMH nozzle

nozzle (b) UMH injection nozzle

upper injection holes cone under injection holes cone

Conventional nozzle UMH nozzle

(a) (b) Fig. 2. Schematic comparison between the conventional and UMH nozzle (a) Conventional Table 1 lists the specifications of test nozzles. It can be seen that the flow rate of the UMH nozzle with smaller diameter hole is higher than that of the original nozzle by up to 67%, which helps the UMH nozzle not only shorten the injection duration and also improve fuel atomization.
