In modern diesel engines, selective catalytic reduction (SCR) technology, is thought to be the most efficient way of removing nitrogen oxides (NOx) from emissions. In this way the system's principal antihypatity is converting injurious nitric oxides in smoke plumes into water vapour and harmless nitrogen, which helps to minimize the environmental impact of exhaust gas. In this scheme, a liquid reductant, often urea, is introduced into the exhaust stream ahead of a catalyst. The catalyst then facilitates the chemical reaction that breaks down the NOx. Critical advances in technology include an SCR catalyst coated with precious metals that promote reduction process, and an advanced dosing system that controls precisely the injection of reductant. Uniship has long experience in selectives catalytic reduction of nitrogen oxides (SCR), its systems are used widely on high-power engines, heavy-duty vans and riverboats to keep up with ever tougher environmental regulations.