Catalyst technology for the diesel engine cars
The catalyst system for diesel engine cars "HC-SCR" detoxifies NOx with unburned hydrocarbon (HC) in the exhaust fumes and the fuel decomposition product HC as a reducing agent. As refilling urea water is unnecessary, it contributes to improve convenience and to save space of the vehicle by eliminating urea tank.
"The law to control harmful substances in exhaust fumes that have a negative influence on ""Environment"" and ""Human body"" is becoming severe all over the world year after year. Especially the control value of ""Nitrogen oxide (NOx)"" in the diesel engine emission is severe because it reacts with ultraviolet rays in the air to a cause of photochemical smog that affects negatively on human body as well as becoming cause of acid rain that has a negative impact on environment. In addition, it is said that purifying NOx in the emissions of diesel engine is very difficult because lack of reducing agent to purify NOx due to high air late (Lean) in the control issue."
"The rate of fuel and air that reacts neither too much or too little is the theoretical air-fuel ratio. Rich: Theoretical air-fuel ratio less than 14.7.. (More fuel) Lean: Theoretical air-fuel ratio 14.7 or more. (More air) It's possible to control fuel and air close to the theoretical air-fuel ratio with the gasoline engine but it becomes ""Lean"" status with the diesel engine due to the system of spontaneous combustion by high temperature in the cylinder. "
As for correspondence by the engine control, there is a limit, and purification with the catalyst is required for the nitrogen oxide (NOx) effluent standard that is becoming severer. Urea SCR system is one of the exhaust gas purification technologies to purify NOx under the exhaust of the diesel engine. SCR is abbreviation of Selective Catalytic Reduction. The reducing agent is needed to purify NOx and ammonias are becoming a main current being paid attention as the reducing agent It was applied that ammonia (NH3) was reduced to nitrogen (N2) and water (H2O) by chemical reaction with NOx taking a hint from. Exhaust gas processing system of the thermal power plant and the ship. However, a tank with urea water is equipped in the car to hydrolyze and obtain ammonia gas under the high temperature by injecting urea water in the exhaust fumes because loading ammonia in the vehicle is dangerous
Many of the diesel engine vehicles adopt the Urea SCR system as an aftertreatment device of diesel heavy vehicles in Japan, developed countries in Europe and U.S. as of 2018. But the actual situation is that the area and car type are limited because users have to refill urea periodically. Preparing infrastructure of urea is the challenge item of the Urea SCR.
Small-medium size trucks are used mainly in a small area compared to the large size trucks. If there is no infrastructure of urea in that area the trucks have to move wherever to refill. In emerging countries, preparation of the infrastructure of urea cannot keep up with because the economy has drastically developed and number of vehicles have drastically increased.
In addition, it needs to make a space for the urea tank in the truck.
"Refilling urea and space for the tank are not necessary with the HC-SCR system because the fuel (HC) is used as a reducing agent. Therefore, it is effective system especially for medium-small size trucks."
As it is possible to purify NOx in wide temperature range by changing active species M uniquely, we have achieved equivalent NOx emission to it of Urea-SCR system in the catalytic reaction of HC-SCR system.
Urea tank, urea supplying device, SCR catalyst are not necessary on the vehicles mounting HC-SCR system. In addition, compact aftertreatment system is excellent for installation and mountability. They make it possible to meet the needs of the wide range of users.
"It has achieved reduction of the cost by 30%, weight by 80kg and space by 50L compared to the urea SCR system of the existing 4t truck. Domestic production result of the mid-small size trucks is 720,000 since start of sales in 2010. It is possible to reduce fuel consumption for PM combustion and regeneration on DPF by 28% of the mid-small size trucks. Therefore annual usage of the light oil can be reduced 4.5kL and reduce CO2 11,600 tons based on the estimation of the reduction of annual fuel usage for driving mid-small size trucks. This aftertreatment system has been adopted to deal with the domestic post new long-term regulation and it is possible to adapt the emissions regulations that will be introduced to the emerging countries in the future. This technology is expected to be expanded in the Asian and emerging countries that the infrastructure of urea hasn't been prepared yet."