The science of Tier 4

Aug 1, 2008 12:00 PM

Solution EGR

EXHAUST GAS RECIRCULATION with a diesel oxidation catalyst (DOC) and diesel particulate filter (DPF) — This technology diverts a percentage of the exhaust gas back into the cylinder, lowering combustion temperatures and reducing the amount of oxides of nitrogen. The DOC reduces carbon monoxide, hydrocarbons and some particulate matter. The downstream DPF component traps and holds particulates remaining in the exhaust stream.

Trapped particles are eventually incinerated within the DPF through a process known as “regeneration.”

(SCR) — This system for gas and diesel engines is designed to reduce oxides of nitrogen emissions by injecting urea into the exhaust stream.

Right: In 2007 at Agritechnica, an international farm show in Germany, Sisu Diesel unveiled its first Tier 4 technology diesel engines, which use SCR to reduce emissions. AGCO uses these engines in vehicles designed for forestry applications.

SCR TREATS the exhaust gas after it leaves the vehicle by injecting a special solution, typically urea, into the exhaust stream to reduce the NOx emissions emitted by the engine. The urea solution is carried in a separate tank located close to the main fuel tank. A common brand of urea is AdBlue.