Analysis of strengthening local cooling on diesel cylinder head using nano-fluids with jet impingement technology

Abstract: Diesel engines, as an important power source for machinery, are increasingly subject to people's attention. Only with better cooling systems can they put up better work performance. Because coolant flow in the cylinder heads is difficult, how to better cool this part is becoming a hot point in the researching world. To solve the problem of cooling the high heat density areas in diesel cylinder heads, our study used nanofluids with jet impingement technology, due to better capacity of heat transmission of nanofluids and better capacity of local cooling of jet impingement technology. Thoroughly configuring different volume ratios of nanofluids, using the nanoparticles Cu, MgO, and Al2O3, we researched the change regulation of the heat transfer ability of diesel cylinder heads with self-made jet impingement equipment. The results showed that, compared with traditional coolant, using three kinds of nanofluids with jet impingement can enhance the heat transfer performance several degrees at high heat density areas in the cylinder heads. With proper setting of the jet impingement parameters, the largest local ratio increase was 110%. Different volume ratios of nanofluids took different variation trends of the heat transfer coefficient. In the volume ratio of less than 2%, the jet heat transfer coefficient of nanofluids decreased with particle concentration, and with the further increase of particle concentration the heat coefficient continued to decrease. This increase in nanoparticles increased the viscosity level of the nanofluids, resulting in decreased fluid flow. With the increase of jet velocity, the heat transfer coefficient of the nanofluids increased, but the heat transfer coefficient of MgO was the lowest at low-speed, even lower than traditional coolant at 2% ~ 4%; the viscosity number of MgO nanofluids was the largest, so too low of a jet speed can make fluid flow difficult. With the increasing jet height, the heat transfer coefficient of nanofluids also increased, but the exorbitant jet height was counterproductive. Different jet heights created a varying jet impingement spread, yet only a suitable jet distance can produce better heat transfer. With the increase of jet angles, the heat transfer coefficient of nanofluids increased, but when jet angles decreased, the heat transfer coefficient of nanofluids not only were decreased but also took the phenomenon of inconsistent temperature. Too small of a jet angle made the maximum gap of nearly 30℃ from different test points, that is to say, different test point existed different test temperature. This phenomenon of temperature inconsistencies made this new technology engineering application limited. Jet heat transfer coefficient increased with initial temperature, but after 65℃, the heat transfer coefficient is decreased with increasing initial jet temperature. The increase of the concentration of particles also increases the power consumption of the electric pump. The maximum power loss was 115 W in testing; if this technology is desired in engineering applications, the researchers must think of better ways to minimize this kind of power loss as much as possible. The results of this research, as an application based research, provides new research ideas for better cooling of the cylinder heads' local high heat density area.