Li, J., Ge, Y., He, C., Tan, J. et al., "The Application of Solid Selective Catalytic Reduction on Heavy-Duty Diesel Engine," SAE Technical Paper 2017-01-2364, 2017.
Urea SCR technology is the most promising technique to reduce NOx emissions from heavy duty diesel engines. 32.5wt% aqueous urea solution is widely used as ammonia storage species for the urea SCR process. The thermolysis and hydrolysis of urea produces reducing agent ammonia and reduces NOx emissions to nitrogen and water. However, the application of urea SCR technology has many challenges at low temperature conditions, such as deposits formation in the exhaust pipe, lack deNOx performance at low temperature and freezing below -12°C. For preventing deposits formation, aqueous urea solution is hardly injected into exhaust gas stream at temperature below 200°C. The aqueous urea solution used as reducing agent precursor is the main obstacle for achieving high deNOx performances at low temperature conditions. This paper presents a solid SCR technology for control NOx emissions from heavy duty diesel engines. The solid SCR technology, using a solid metal ammine complex to store ammonia, can overcome the issues of urea SCR by dosing gaseous ammonia directly to the exhaust gas steam. In this paper, the applications of solid SCR for a CN-5 heavy duty diesel engine and a CN-4 heavy duty diesel vehicle was discussed based on engine bench tests and portable emission measurement system tests, a comparison study on NOx emission was performed with urea SCR during real world driving conditions. The results showed that the solid SCR technology could promote the deNOx performances more efficiently than urea SCR technology at low temperature conditions.