Journal of Mechanical Science and Technology 26 (4) (2012) 1265~1274 www.springerlink.com/content/1738-494x DOI 10.1007/s12206-012-0208-y Experimental analysis of emission reduction by the split injection strategy using close post injection with a double-row nozzle in heavy EGR conditions † Jeongwoo Lee 1 , Seungmok Choi 1 , Seunghyup Shin 1 , Hoimyung Choi 2 and Kyoungdoug Min 1,* 1 School of Mechanical and Aerospace Engineering, Seoul National University, Gwanak-Gu, Seoul, 151-744, Korea 2 Advanced Institutes of Convergence Technology, 864-1 Youngtong-gu, Suwon 443-270, Korea (Manuscript Received May 18, 2011; Revised September 30, 2011; Accepted December 5, 2011) ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Abstract As EURO-6 regulations will be enforced in 2014, simultaneous reduction of NOx and PM emissions becomes an important issue in re- cent diesel engine research. New combustion concepts, such as LTDC and pHCCI, have been introduced to overcome the NOx and PM trade-off relation. However, these novel combustion concepts are usually implemented with a high EGR rate and by advancing the main injection timing which cause high CO and THC emissions along with poor fuel consumption due to low combustion efficiency. There- fore, the split injection strategy, which was consisted of applying post injection close to the main injection, was carried out in this ex- periment. Specifically, two different nozzles – a 7-hole conventional nozzle and a 12-hole double-row nozzle – were evaluated to deter- mine the effects of nozzle configurations on engine-out emissions. The result shows that CO emission was reduced by the close post injection strategy regardless of the nozzle configuration. However, THC and PM emissions were reduced only when the 12-hole double- row nozzle was used. Thus, the use of close post injection with the 12-hole double-row nozzle could increase the combustion efficiency in heavy EGR conditions. Keywords: Carbon monoxide; Close Post injection; Exhaust gas recirculation; Multi-row nozzle; Nitrogen oxides; Unburned hydrocarbon ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- 1. Introduction Currently, the reduction of engine-out emissions is focused on novel combustion technologies of diesel engines because automotive emission regulations are becoming increasingly stringent. Specifically, EURO-6 will be enforced in 2014, which mandates that the emission of NOx be reduced as a half of EURO-5 standard. Exhaust gas recirculation (EGR) is one of the most effective ways of controlling both the combustion and emissions of a diesel engine. Increasing the EGR rate raises the specific heat capacity as a thermal effect and lowers the O2 concentration as a dilution effect of the trapped gas in the same boost condi- tion. It lowers the flame temperature [1, 2] and delays com- bustion (by delaying ignition, premixed combustion and diffu- sion combustion) [3]. As the EGR rate increases, NOx emis- sion is reduced due to the decrease in O2 concentration and the lower burnt gas temperature. However, these conditions prevent soot from oxidizing and generally produce more PM. This phenomenon is the so-called “NOx-PM trade-off”. One way of reducing NOx and PM emissions simultane- ously is homogeneous combustion. Forming homogeneous mixtures can eliminate PM emission, and it is achieved by improving the injection strategy or the piston bowl shape. Uniform bulky combustion system (UNIBUS) is one example of homogeneously mixing air and fuel [4]. UNIBUS can be implemented by performing the main injection early, at BTDC 50 CA, and the secondary injection at ATDC 13 CA. The fuel that is injected earlier mixes homogeneously with the air, and the subsequently injected fuel acts as a trigger for ignition. This dual-injection strategy has the benefit of reducing NOx and PM emissions because the duration of the pre-mixture is enough to form a homogeneous mixture. The other example of homogeneous mixing is “modulated kinetics” (MK) com- bustion [5]. The goal of this technique is to extend the ignition delay to exceed the injection duration to allow enough mixing time between the air and the fuel. To do this, the main injec- tion timing is delayed with a high EGR rate and high swirl ratio. Another approach to reduce both NOx and PM emissions is to achieve low temperature diesel combustion (LTDC) to avoid generating NOx and PM. If the EGR rate is extremely high, the combustion temperature will be under 1,600 K due to thermal and dilution effects. In addition, the air and fuel mixture would become richer because of the low oxygen amount relative to the fuel [6, 7]. A concept related to LTDC * Corresponding author. Tel.: +82 2 880 1661, Fax.: +82 2 883 0179 E-mail address: kdmin@snu.ac.kr † Recommended by Associate Editor Tong Seop Kim © KSME & Springer 2012