Abstract
The regulation of harmful emission including CO2 is getting more strict recently according to greenhouse gases problem caused by increasing of CO2 emission.
The Diesel engine provides many positive aspect such as higher thermal efficiency and less CO2 emission. However, there are some problem on PM and NOX emissions. PM(Particulate Matters) has decreased by around 90% according to development of DPF technology. NOX reducing technique such as LNT, LNC, SCR has been developed and applied especially on heavy duty vehicle. But it is expected the NOX reducing technique is applied on passenger diesel vehicle, as well. The Urea-SCR system is getting attention as the most effective NOX reducing technology without fuel efficiency incline, so that many advanced countries are developing this technology. Urea-SCR system sprays Urea- aqueous solution to take apart into N2 and H2O and emit into the atmosphere as reducing agent which is harmless. Injected Urea in front of SCR catalyst should be changed to NH3 100% required for NOX reduction in SCR system to maximize reducing efficiency.
In this study, NOX reduction rate and NH3 slip were compared depending on α ratio with application of Urea-SCR system on the passenger diesel engine mounted with only HP-EGR and the engine mounted with HP-EGR and LP-EGR with the same base.
In conclusion, NOX reduction rate and NH3 Slip showed the difference when the same Urea-SCR system was applied on each engine. The higher NOX reduction rate was shown in the engine mounted with HP-EGR, and NH3 slip was higher too. Also, it was confirmed that reduction effect was continued longer while NOX reduction rate was increased as α ratio was increased.
Due to this system, It can be a strategy to reduce Particulate Matter and products of incomplete combustion in combustion process. As a result, It can satisfy not only Euro-6 regulation but future regulations. But it was considered that the strategy of post-injection seemed to be necessary for increasing exhaust temperature to reach to the activation temperature of SCR catalyst to adopt the Urea-SCR system in the passenger diesel engine with LP-EGR to cope with the emission regulating in the future.
KEYWORDS – Passenger diesel engine, Urea-SCR, NOX reduction rate, NH3 slip, HP/LP-EGR, Exhaust temperature