Diesel Emissions

Clean diesel emissions are extremely important to our planet; therefore, we need to be able to understand the effects of diesel emissions. The result of complete combustion is water (H2O) and carbon dioxide (CO2). Both of these are natural parts of our environment, although some scientists believe that CO2 in high concentrations acts as a greenhouse gas. At this time, the only way to reduce CO2 emissions on diesel engines is to reduce the amount of fuel burned. This can be accomplished by making engines and vehicles more fuel efficient, or by driving them less.

The most deadly pollutant is carbon monoxide. Carbon monoxide is a result of partially burned diesel fuel and is a serious health hazard to humans because it can reduce oxygen delivery to organs and cause death.

FIGURE 54-8
The electronic diesel control (EDC) has a processing unit and input and output devices.

Two additional exhaust emission pollutants we are concerned with actually mix with sunlight to form ozone (smog) and acid rain. They are hydrocarbons and nitrogen oxides. Hydrocarbons, or unburned fuel, are the result of incomplete combustion. Nitrogen oxides are the result of high temperature combustion.

Diesel-powered vehicles are increasing in popularity at a rapid rate around the globe. One of the main reasons for this rise in popularity is the emergence of electronic diesel control (EDC). This system uses a processing unit (computer) in conjunction with input and output devices to accurately control fuel delivery in modern diesel engines Figure 54-8.

EDC has enabled cleaner, more complete combustion with lower emissions, greater economy and power, and lower noise levels not previously achievable with either direct or indirect combustion chambers. In modern diesel engines, soot emissions, properly called particulate matter, have been reduced by up to 83%. Nitrogen oxide emissions resulting from the heat of combustion have been reduced by 63% since 1988. Moreover, hydrocarbon, carbon monoxide, and carbon dioxide emissions, already inherently low with diesel engines, have improved—with the trend set to continue.

FIGURE 54-9
A diesel particulate filter (DPF).

Since 2007, all highway diesel engines have been required to have a diesel particulate filter (DPF) Figure 54-9. Its job is to convert particulate matter, or soot, into ash. Soot can best be described as unburned particles left over from the combustion process. Ash is what is left after the soot has been incinerated. The conversion is accomplished through a catalytic process in the DPF. Often, it takes additional fuel with a spark or high temperatures to complete the process. After time, the ash builds up in the DPF and needs to be removed. This service interval is typically 150,000 miles (240,000 kilometers [km]) for an on-road vehicle.

Another clean diesel technology is called selective catalytic reduction. It is an active emission control system that injects a liquid reductant, or reducing agent, through a special catalyst into the exhaust stream of a diesel engine. The reductant, or reducing, agent is urea, which is a chemical reactant specifically designed for use in selective catalytic reduction systems to reduce nitrogen oxides. In the industry, urea is called diesel exhaust fluid (DEF). It causes a chemical reaction that converts nitrogen oxides into nitrogen, water, and very small amounts of carbon dioxide, which is exhausted through the tailpipe.

”Clean diesels” have the ability to completely and efficiently burn fuel within the engine. Additional benefits include quieter engines with a higher horsepower to weight ratio. The primary enhancements include improved fuel delivery systems, improved configuration of combustion chambers, and turbocharging.