Heat loss is one of the main causes of energy losses in modern direct injection diesel engines. This heat loss of the engine occurs during combustion, mainly due to the heat transfer between the impinging spray flame and the piston cavity wall. It is of more critical in small size engines. In order to decrease heat transfer, we need to examine the phenomenon of heat transfer through the combustion chamber walls more fully. To achieve this, we investigated the effects of flame impingement on transient heat flux to the wall. By using a constant volume vessel with a fixed impingement wall, the surface heat flux of the wall at the locations of spray flame impingement was measured with three thin film thermocouple heat flux sensors. The combined effect of impingement distance and injection pressure on the heat transfer was investigated parametrically. The results showed that an increase of injection pressure with longer impinging distance led to an increase in the heat transfer coefficient, which had a dominant effect on local heat flux compared with local temperature distribution. Moreover, we confirmed that the relation between Nusselt number and Reynolds number is a useful measure for describing the heat transfer phenomena in diesel combustion.

Reducing heat loss is one of the most important development concerns for improving the thermal efficiency of the diesel engine. In order to know heat transfer through the combustion chamber wall more clearly, the effects of flame impingement on transient heat flux to the wall were investigated. Using a high-pressure and high-temperature chamber under diesel engine–like conditions, fuel was injected from a single-hole injector against an impingement wall. Surface heat flux of the impingement wall was measured by temperature with three thin film thermocouple heat flux sensors. Simultaneously, luminous flame, flame temperature, and soot distribution were also investigated. The results showed that temperature near the wall and flame contact area have great influence on the local heat flux. Furthermore, local heat flux, combustion, and soot formation reached maximum levels at some spray impingement distance to the wall.

<div class="section abstract"><div class="htmlview paragraph">Substantial amount of fuel energy input is lost by heat transfer through combustion chamber walls in the internal combustion engines. Thus, these heat losses account for reduced thermal efficiency, in that spray-wall impingement plays a crucial role in Direct Injection diesel engines. The objective of this study is to investigate the mechanism of the heat transfer from the spray/flame to the impinging wall under small diesel engine-like condition and how the spray characteristics are affected with regards to effect of injection pressure, nozzle hole diameter and impingement distance. The experiment results showed that injection pressure was predominant factor on spray-wall heat transfer.</div></div>

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Experimental and numerical research have been performed to investigate the Wavy Leading Edge (WLE) effect on the rectangular wing. The WLE is inspired by humpback whale flipper morphology which is blunt and rounded in certain form pattern. This flipper shape plays an important role for its behaviour specially capturing their prey. This advantage could be applied to other systems such as fin stabilizers or wind turbines. Steady cases in various aspect ratios were conducted to find out the optimum effect of WLE with baseline NACA 0018 profile at Reynolds number 1.4 x 105. The chord length of the wing (c) was 125 mm. The WLE shape defined as wavelength (W) 8% of c and amplitude (d) is 5% of c. The aspect ratio (AR) variations were 1.6; 3.9; 5.1; 7.9 and 9.6.  A simple rectangular form of the wing was selected to analysis the WLE effect on the various ARs. The taper wing shape is applied to find out the WLE effect at the AR 7.9. three types of taper ratio (TR) are 0.1; 0.3 and 0.5. The results show that the WLE on the taper wing has better advantage to control the stall in steady case. Another impressive result was the WLE wing with AR 7.9 and TR 0.3 has the best lift coefficient and pressure distribution.Keywords: stall, wavy leading edge, steady case, rectangle wing, taper wing, aspect ratio.

The objective of this study is to obtain an enhanced understanding of the effect of diesel spray/flame impingement on transient heat flux to the wall. By using a constant volume vessel under engine-like condition, surface heat flux of the wall at spray/flame impingement was measured with three thin film thermocouple heat flux sensors. Fuel was injected using a single-hole injector with a 0.133 mm diameter nozzle. In order to investigate the relation between diesel flame and wall heat loss, two color-method was applied to observe flame temperature distribution. 21 % and 16 % as the various oxygen concentration were investigated at each injection pressure of pressure 80, 120, and 180 MPa. The results showed that the lower oxygen concentration was generated heat loss regardless of injection pressures. The lower flame temperature and flame contact area and period were influence factor on heat loss on the wall. Furthermore, the relation between Nusselt number (Nu) and Reynolds number (Re) were also investigated to understand the heat transfer phenomena in diesel engines.

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