Tier 4 emissions reductions through EGR
Particulate matter refers to the smoke coming out of the exhaust pipe which is primarily due to incomplete combustion of diesel fuel. Nitrogen oxide emissions are called smog and contribute to the pollution in the outside environment. The two ways with which to reduce these emissions is through cooled exhaust gas recirculation (EGR) and an exhaust filter. EGR reduces nitrogen oxide emissions while the exhaust filter reduces particulate matter. Tier 4 emissions reduction through EGR cools and mixes measured amounts of exhaust gas with the fresh air that gets inside the engine to lower the engine’s peak combustion temperature so as to reduce nitrogen oxides within an acceptable level. However, the reduction of nitrogen oxides increases the amounts of particulate matter which requires the exhaust gas to pass through an exhaust filter that contains a diesel oxidation catalyst and a diesel particulate filter. The diesel particulate filter will trap particulate matter and through the process of regeneration it will be oxidized into nitrogen gas, water and small amounts of carbon dioxide that will be expelled through the exhaust pipe.
Tier 4 emissions reduction through SCR
In an effort to provide the most reliable technology for emissions reductions, manufacturers are turning to SCR technology to meet the high horsepower Tier 4 emissions reduction requirements. The SCR system is based on an ammonia solution referred to as diesel exhaust fluid (DEF) and also known as urea that is injected into the exhaust system downstream of the turbocharger where it converts into ammonia. This gas mixture reacts with nitrogen oxide when it passes over the SCR catalyst to produce a harmless mixture of water vapor and nitrogen gas. Unlike the exhaust filter, the SCR system does not require cleaning and maintenance under normal conditions. The levels of nitrogen oxide can be measured through a closed loop system both upstream and downstream of the catalyst so as to ensure the highest levels of reliability.
The impact of Tier 4 emissions standards
Over the past years, regulations of diesel engine emissions only covered trucks and buses but in January 01, 2011, regulations were harmonized for stationary diesel engine emissions with mobile non-road emissions. EPA has tightened the requirements on the first set of emission regulations that were known as Tier 1 so as to encourage engine manufacturers to make use of technological advancements to meet the latest Tier 4 emissions standards. Currently, Tier 4 emissions are the strictest among EPA requirements for off-highway diesel engines used in power generations, industrial applications, oil and gas applications, mining operations and mobile equipment.