Emission Control Technologies in Compression Ignition Engines

Emission Control Technologies in Compression Ignition Engines

The need to control emissions comes as a result of new standards proposed by the EPA (Environmental Protection Agency). The Draft RIA (Draft Regulatory Impact Analysis) provides economical, technical, and environmental analysis for compression ignition engine (Jackson, 2012). The anticipated reduction is meant to reduce emission of gases that have a negative impact on the environment, which includes hydrocarbons (HC), oxides of Nitrogen (NOx), particulate matter (PM) and carbon monoxide (CO).

In 2002, the regulatory board adopted verification procedure that involved in-Use Strategies to help reduce emissions from diesel engines (Jackson, 2012). The verification procedures defined a clear process, which manufacturers handling emission control equipments can follow, and demonstrate reduction capabilities in their control technologies. There are several technologies that are currently available and useful in controlling diesel particulate matter from portable diesel engines Some examples of control technologies that can be employed includes fuel oxidation catalyst, fuel particulate filter, selective catalyst reduction system, exhaust gas recirculation, alternative diesel fuel systems, and fuel additives (Mahgoub, Sulaiman & Karim, 2012). Majority of these methods are currently being verified by the ARB portable diesel engines and on-road vehicles. Currently, the only technology that has been verified by ARB for off-road engine use is the diesel oxidation catalyst.

Fuel particulate filters reduce fuel PM emissions through the process of filtration. This technology has demonstrated great efficiency, and has been used to reduce diesel PM by almost 90% (Mahgoub, Sulaiman & Karim, 2012). There are several classes for fuel particulate filters, which include active, passive, and flow-through.

Passive fuel particulate filters make use of catalytic material that enables the trapped PM to be oxidized or burned-off at lower temperatures. In order for this system to be effective, the exhaust must maintain a minimum temperature when the engine is operating for certain duration (Mohanamurugan & Sendilvelan, 2010). Otherwise, there will be accumulation of diesel or fuel PM in the filter causing operation problems. There are several fuel particulate filters that have been verified for on-road purposes. However, there are no fuel particulte filters that have been verified for application on the portable engines.

Active fuel particulate filter function the same as passive fuel filters but differ in the sense that they oxidize by using heat from the engine exhaust. Flow through the filter (FTF) technology is a current technology that is being employed to reduce PM emissions. In this method, the exhaust is allowed to move through certain media, such as wire mesh with high density causing turbulent flow conditions (Mahgoub, Sulaiman & Karim, 2012).

Various emission control strategies have been employed on land-based nonroad, locomotives, and on-highway engines. The strategies used to reduce exhaust emission include better fuel control, combustion optimization, exhaust gas recirculation, after-treatment, and improved charge air characteristic.

Combustion Optimization

There are several parameters present in the combustion chamber of compression ignition engines that affect its emission and efficiency. These parameters include combustion chamber geometry, injection timing, valve timing, turbulence, compression ratio, fuel spray geometry and rate, injection pressure, peak cylinder temperature and pressure, and intake air pressure and temperature (Mohanamurugan & Sendilvelan, 2010). The strategies employed in controlling emissions have proved to be complex because positive influence on one of the polutants causes a negative influence on another pollutant. For example, reduction of NOx using charge air cooling increase PM. Therefore, these complexities require the manufacturers to integrate all the variable present for proper optimization of the systems to meet the proposed standards.

Timing Retard

The effect of ejecting timing on performance and emissions plays a key role in creation of vital strategies for controlling emissions. Retard timing is most likely applied at cruising speeds where compression ignition engines take most of their operating time (Jianyong et al, 2014). NOx emissions are reduced as a result of shortened premixed burning phase and lowered pressure. Timing retard raises CO, HC and fuel consumption, but because the end of injection delays in the combustion stroke, the time required to extract energy from combustion of fuel is reduced and cylinder pressure and temperature reduces for incomplete oxidation of PM (Mohanamurugan & Sendilvelan, 2010). One method that can be employed to offset this trend is using high injection pressure.

Combustion Chamber Geometry

Many manufacturers are modifying combustion chamber in order t 

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