# Exhaust Gas Characteristics According to the Injection Conditions in Diesel and DME Engines
## 1 Introduction  
In order to prevent air pollution caused by exhaust gas from automobiles, exhaust emission regulations such as Tier-III and EURO-VI have been announced in various countries such as USA, Europe and Japan. Many researchers are working to reduce harmful emissions by gradually increasing the allowable regulation of hazardous emissions from automobiles [1]. Diesel engines have been widely used as power sources for automobiles and ships because of their high thermal efficiency and fuel efficiency. It has the advantage of low carbon monoxide (CO) and unburned hydrocarbons (HC) because it burns under lean conditions where the fuel consumption rate is lower than that of the gasoline engine and the combustion state is excess oxygen. However, since it has the disadvantage of high PM (particulate matter) and NOx (nitrogen oxides) emissions, it cannot satisfy the increasingly stringent emission regulations [2; 3]. Using diesel particulate filters (DPF) together with diesel oxidation catalysts (DOC) is a technology that can reduce the emissions of diesel cars to the level of the latest gasoline vehicles. There have been many studies on nitrogen oxides in various countries depending on the social environment and economic conditions. However, in Europe, selective catalytic reduction (SCR) and US prefer the NOx storage catalyst (LNT, Lean NOx trap) [4]. The exhaust emission reduction techniqueusing the above-described exhaust after-treatment apparatus reduces emissions discharged through the engine combustion process to a separate device in the exhaust system. The soot purification apparatus and the NOx storage catalyst are excellent in filtering soot and NOx components, respectively Performance. However, in order to apply the actual engine, it is necessary to remove the accumulated soot or SOx through a process called regeneration while monitoring the state before and after the filter [5; 6; 7]. A number of studies have been conducted to reduce exhaust gases such as nitrogen oxides and soot using various fuel properties and additives [6; 7], multiple injection [8; 9], EGR [10; 11; 12] and PCCI/SCCI/CAI [13; 14; 15; 16]. DME (dimethyl ether, CH3-O-CH3) among alternative fuels for diesel engines has low auto ignition temperature. It also has good evaporative performance when sprayed into the combustion chamber and has a higher cetane number (>55) than the diesel fuel. In particular, DME is an oxygen-containing fuel containing about 34.8 wt% of oxygen, and because there is no direct coupling between carbon and carbon in the fuel characteristics, almost no PM is being emitted in the diesel engine [17; 18; 19; 20; 21; 22; 23]. Due to these advantages, it is possible to apply a large amount of exhaust gas recirculation (EGR) without much difficulty to the engine, and it can greatly reduce NOx, and it has many excellent characteristics as an alternative fuels for diesel engines [24; 25; 26; 27; 28]. This is because it is easy to change and improve parameters affecting injection characteristics such as injection timing, injection duration, and injection pressure and injection quantity independently of engine rotation through electronic control. It is a great advantage to have superior advantages compared to the existing diesel engines such as output, fuel consumption, noise and vibration, and reduction of NOx in exhaust gas through electronic control according to each 4 conditions [29; 30; 31]. Experiments and numerical studies on spray combustion and exhaust characteristics for compression ignition engines using DME fuel have been conducted by many researchers. Numerical studies on compression ignition engines show that the application of diesel alternative fuels is largely dependent on the physical and chemical properties of the fuel and the application of a chemical reaction mechanism for combustion simulation [PERSON] et al. [32] used the results of the study on the thermodynamic properties of DME fuel and the fuel property data of the AVL FIRE program [28] as input to the fuel material subproject of KIVA-3V code.