November 17, 2015

Cooled EGR vs SCR Internal Combustion Temperatures

The distinction between Interim Tier 4 Engine Technology like Cooled EGR and SCR remains a topic of uncertainty. In an effort to provide further clarification, here is a myth on exhaust gas recirculation (EGR) vs. selective catalytic reduction (SCR)-equipped IT4 engines.

Myth: Does a cooled EGR-equipped diesel engine have a higher internal combustion temperature than an SCR-equipped engine?

Fact: As its name implies, cooled EGR cools and mixes measured amounts of exhaust gas with incoming fresh air to lower the engine's peak combustion temperature, thereby reducing nitrogen oxide (NOx) emissions to an acceptable level. The exhaust gases are then routed through an exhaust filter, which traps the particulate matter (PM).

In contrast, engines equipped with SCR technology usually operate at higher combustion temperatures in order to reduce particulate matter to acceptable emissions levels. This places additional heat on the internal components of the engine and creates more NOx. To reduce NOx, a diesel exhaust fluid (DEF) is injected into the exhaust stream, which combines with the exhaust gases in the SCR catalyst.

John Deere's cooled EGR engines actually have cooler internal engine combustion temperatures than SCR engines. Cooled EGR engines do place more cooling requirements (higher heat rejection) on the cooling system; however, John Deere has adopted new variable speed fan drives and cooling system designs for IT4 that meet cooling needs in the most efficient method possible.