Combustion bomb study

The study on the spray combustion characteristics of 10% CPO blended with diesel fuel was conducted in a constant volume combustion chamber. With the fixed experimental conditions such as spray ambient pressure and injection events, the effects of 10% CPO diesel at the injection line pressure of 100 MPa on spray combustion and flame structure were investigated using photo diode and ICCD camera. The two-colour method was also employed to predict combustion flame temperatures and KL factors.

The injection system used in this research was an electronically controlled accumulator type fuel injector system.13,14 With a 0.2 mm diameter single hole injector, driven by a piezo electric actuator via an extended pressure pin, we could control the needle lift and fuel injection rate shaping. The schematic diagram of the injector and details are shown in Fig. 23.1.

Experiments were conducted in a constant volume 2.2 litre vessel with 80 mm diameter quartz observation window on the side, gas mixing propeller on the bottom and injector on the top, as shown in Fig. 23.2. The ambient conditions maintained inside the vessel were high temperature and pressure by igniting hydrogen in an enriched oxygen and air mixture. The oxygen concentration after the hydrogen combustion was approximately 21% by volume.13,14

The rectangular injection rate shaping was obtained in this experiment, as shown in Fig. 23.3. Fuel injection mass was set at approximately 15 mg for all experiments. Injection pressure was 100 MPa. The fuel was injected in the vessel at the ambient conditions of 3.0 MPa, temperature around 900°C, as shown in Fig. 23.4. The calculated composition of ambient gas was O2 20.9%, N2 70.8% and H2O 8.3%.

/Photo diode

* (to detect luminous emission) P. M.T.

(To measure OH radical photoemission in flame)

23.2 Experimental apparatus.

After the hydrogen combustion, the fuel was injected into the vessel and then combusted. Fuel spray combustion flame photographs were taken by ICCD camera. Light emission of flame was measured using two photo sensors: a photo multiplier tube with a band-pass filter centres on a wavelength of 310.3 nm (FWHM: 16.3 nm) was used for measuring the intensity of OH radical emission and two photo diodes (used for measuring the luminous light intensity) at the upper and the middle of observation window. The start of spray was detected by the combination of the use of He-Ne laser with photo sensor. Using photo diode data, then the ignition delay and combustion period were evaluated.

23.4 Temporal variation of gas pressure inside the vessel.15

The two-color method was applied to estimate two dimension (2D) contour of temperature and KL factor (KL factor is the factor used to indicate soot) distribution in the combustion flame. This two-colour pyrometry system was set up by placing Vari lens that has the two-different band-pass filters 488 nm in centre wavelength (FWHM: 11.3 nm) and 634 nm in centre wavelength (FWHM: 8.5 nm) for separating image to be two in front of an ICCD camera lens. The intensity data of both filters were used to calculate the true temperature and KL factor.

The data obtained from He-Ne laser and OH-radical were used to calculate ignition delay. It was found that 10% CPO diesel gave shorter ignition delay compared with diesel as shown in Fig. 23.5.

The data 10% of peak intensities obtained from the two photo diodes were selected to be the start and end of the combustion. The result shows that the observed combustion period of 10% CPO diesel at injection pressure of 100 MPa was slightly shorter than diesel as shown in Fig. 23.6.

The amount of injection fuel became slightly smaller and the injection period became slightly shorter with the 10% CPO diesel due to the higher viscosity of 10% CPO diesel.

The exposure time of ICCD camera was set at 10 psec.15 The spray combustion flame intensity data complied with two colour method.16 Some of the calculated results of true temperature are shown in Fig. 23.7.

The calculated data obtained from spray combustion flame true temperature were used for calculating the KL factor, the factor for indicating amount of combustion soot in flame. The calculated results are shown in Fig. 23.8.

о ID in E

ID Q.

О О

————————- 1—————————— Diesel 10% CPO diesel

23.6 Fuel spray combustion period with injection pressure of 100 MPa at ambient conditions of 3 MPa.15

Total KL factor is the summation of KL factor over the spray combustion flame area. This factor could be used to estimate the total soot of the combustion.

It was found, as shown in Fig. 23.9, that the difference in total KL factor between diesel and 10% CPO was very small.

The average KL factor, shown in Fig. 23.10, was calculated from the total of KL factor divided by spray combustion flame area at all flame area. This factor could be used to estimate the soot concentration of the spray combustion. The

23.7 Spray combustion flame temperature distribution.

23.8 KL factor distribution.

23.9 Total KL factor of palm diesel 60% and diesel fuel at an injection pressure of 100 MPa and 60 MPa.

Time after start of injection (msec) 23.10 Average KL factor of palm diesel 60% and diesel fuel at an injection pressure of 100 MPa and 60 MPa.

results have shown that the difference of average KL factor between diesel and 10% CPO was very small.

Histograms of temperature and KL factor were calculated by evaluating the value from the counted number of spray combustion flame pixel and converting them to flame area (mm2). The interval of temperature and KL factor were selected at 50 K and at 0.005 A. U., respectively. The results are shown in Fig. 23.11.

23.11 Flame temperature and KL factor histogram of palm diesel 60% and diesel fuel at an injection pressure of 100 MPa and 60 MPa.

It was found from temperature histogram that spray combustion of 10% CPO started with lower temperature than diesel. Spray combustion temperature had increased close to diesel during the mid range of combustion period. Then, it became lower by the end of combustion. However, the differences were very small.

The KL factor histogram of Thai palm 10% CPO had no significant difference compared to diesel. Hence, it could be concluded that the difference in soot emission could be very small.

The effects of 10% CPO diesel at an injection pressure of 100 MPa on spray combustion and flame structure were investigated. It was found that diesel blending with 10% CPO has shorter ignition delay and shorter combustion period compared with conventional diesel fuel. High temperature combustion area (over 2400 K) of 10% CPO diesel was also smaller than diesel, especially at the end of the combustion period. The amount of soot and soot concentration affected by this blending percentage may not be significantly different from the diesel fuel.