Journal of Mechanical Science and Technology 23 (2009) 1866~1870 www.springerlink.com/content/1738-494x DOI 10.1007/s12206-009-0616-9 Journal of Mechanical Science and Technology Investigation of emission characteristics affected by new cooling system in a diesel engine † Kyung-Wook Choi, Ki-Bum Kim and Ki-Hyung Lee * Department of Mechanical Engineering, Hanyang University, Seoul, 133-791, Korea (Manuscript Received March 24, 2009; Revised April 30, 2009; Accepted May 1, 2009) -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Abstract In a typical cooling system of automotive engine, a mechanical water pump is used to control the flow rate of coolant. However, this traditional cooling system is not suitable for a high efficiency performance in terms of fuel economy and exhaust emission. Therefore, it is necessary to develop a new technology for engine cooling systems. These days, the electronic water pump is spotlighted as the new cooling system of an engine. The new cooling system can provide more flexible control of the coolant flow rate and the engine temperature, which used to be strongly relied on the en- gine driving conditions such as load and speed. In this study, an engine experiment was carried out on a New European Drive Cycle (NEDC) with a 2.7L diesel engine. The electric water pump operated by BLDC motor and the electronic valve were installed in the cooling system to control the coolant flow rate and temperature. This paper explains that the exhaust emissions were reduced with an increase in the engine temperature and a decrease in the coolant flow. From this experiment, we found that increasing coolant temperature had a significant effect on reducing the emissions (e.g. THC and CO). Decreasing coolant flow also affected the reduction of emissions. In contrast, NOx emission was ob- served to increase in these conditions. Keywords: Engine cooling system; Electric water pump; Fast warm up; Exhaust gas emission -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 1. Introduction A typical automotive engine cooling system has three major components, namely, a mechanical water pump, cooling fans, and a wax-type thermostat. [1-5] These components are not independent of various engine driving conditions. The pump and fans are coupled with a crank shaft by belts, thereby being subject to the engine operating speed. [7-10] Further- more, the mechanical cooling pump is not able to sup- ply sufficient flow for cabin heating at idle condition because of its low efficiency. [11] With respect to the thermostat, its opening and closing relies only on thermal expansion of wax. This gives rise to some shortcoming such as high pressure drop, slow response time and hysteresis. For these reasons, a flexible con- trol of engine temperature is in great difficulty with current cooling technology in our hands. Fortunately, technologies on electronic pumps and actuators have been considerably developed; hence, such difficulty could be easily solved by replacing the mechanically driven system with electronically controllable one. [11, 12] Our strategy in this study was basically to employ electronic equipments that could control the coolant temperature and flow rate more flexibly. The strategy was expected to promote combustion performance in the aspect of fuel saving and emissions penalty. With such goal in mind, engine experiments were per- formed with a new cooling system containing an elec- tric water pump (EWP) and electronic water valves. The experiment was also accomplished during warm- up period under the NEDC operating mode to explore how much the renovated cooling system could con- †This paper was presented at the 7th JSME-KSME Thermal and Fluids Engineering Conference, Sapporo, Japan, October 2008. * Corresponding author. Tel.: +82 31 400 5251, Fax.: +82 31 400 4064 E-mail address: hylee@hanyang.ac.kr © KSME & Springer 2009