Abstract
Reactivity control compression ignition engines illustrated suitable abilities in emission reduction beside high thermal efficiency. In this research, nine various direct fuel injection strategies were studied numerically: three cases with single injection strategy and six cases with split injection and different start of injection (SOI). In all simulated cases, equivalence ratio kept constant (i.e., 0.3). Among various strategies, single injection showed higher IMEP as a factor of efficiency with about 5.39 bar that occurred at SOI = 60 before top dead center (bTDC), while lower efficiency was observed for split injection case with 50%-50% injections of fuel in each injection stage. Start of combustion (SOC), burn duration and CA50 as factors for combustion characteristics were affected with SOI changes. In single SOI strategies, more advanced injection caused more advanced SOC where there was about 1.3 CAD advancing from 40 to 80 bTDC injection. Spilt SOI showed more advanced SOC, which, also more advanced, was allocated to 50%-50% split injection strategy. There was also the same trend in CA50 changes during change in SOI. Burn duration variations were insignificant and all of them approximately close to 4.5 CAD. According to the emissions researched in this study (Nitrogen Oxides (NOx), monoxide carbon (CO) and unburned hydro carbons (UHC)), all of these pollutants are below euro six diesel standards. Contours of emissions show that there were appropriate SOI for each case study, which were 45 degree bTDC for single strategy, 48 degree bTDC for 80%-20% mass injection and 70 degree bTDC for 50%-50% cases.
Highlights
Introduction iationsReactivity controlled compression ignition (RCCI), homogenous control compression ignition (HCCI) and pre-mixed controlled compression ignition (PCCI) are considered as three methods of low temperature combustion (LTC) as methods to have lower emissions in the direction of lower temperature and lean combustion [1]
IMEP was used as a factor for investigations on efficiency; according to this factor tabulated in Table 7 for each of the studied cases, there is better condition in single start of injection (SOI)
It seems that higher time between two SOI decreased IMEP, which was shown in Figure 6 with 50%-50% split strategy, has lower IMEP than the two other strategies
Summary
CFD model in CONVERGE Studio was used to simulate engine combustion and emissions. V pre-chamber (Ricardo plc, Shoreham-bySea, UK); based on this experimental setup, the numerical model of this engine was used during CFD modeling. Specifications of this engine are presented in Table 1; according to this table compression ratio of this engine is 17.2, considering pre-chamber. Combustion quality and thermodynamic properties were affected with heat transfer between chamber and pre-chamber contents and walls heat transfer influences According to this phenomenon, different effective factors were modeled such as flow turbulence, wall heat transfer and gas density change. With CONVERGE Studio’s ability of autonomous mesh generation, mesh creation was done in each time step of solution according to embedded sections, which are prechamber, head, throat and pistons as boundaries and nozzle as in flow embedded area in this modeling
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