Refresher Course on Tier 4
Seven Tier 4-related terms you should know:
- Particulate matter (PM) is made of minute particles dangerous to your health.
- Nitrogen oxides (NOx) are a group of gases that are composed of nitrogen and oxygen that contribute to nitrogen dioxide in the ambient air, acid rain, and the ground-level ozone.
- Selective catalytic reduction (SCR) is a system that injects DEF through a special catalyst into the exhaust stream of the engine. The DEF sets off a chemical reaction that converts NOx into nitrogen, water, and tiny amounts of carbon dioxide, natural components in the air. These are then expelled through the tailpipe.
- Exhaust gas recirculation (EGR) reduces NOx by recirculating small amounts of exhaust gases into the intake manifold where they mix with the incoming air/fuel charge. By diluting this mixture, peak combustion temperatures and pressures are reduced, which reduces NOx output.
- Diesel particulate filter (DPF) is a porous ceramic, cordierite substrate, or metallic filter that physically traps PM and removes it from the exhaust stream. An example of a DPF is shown above.
- Diesel exhaust fluid (DEF) is a nontoxic fluid composed of purified water and automotive grade aqueous urea.
- Diesel oxidation catalyst (DOC) is a flow-through honeycomb structure that is coated with a precious metal catalyst and surrounded by a stainless steel housing. As hot diesel exhaust flows through the honeycomb, the metal coating causes a catalytic reduction that breaks down PM. DOCs can be coupled with other technologies for additional emission reductions.
Life after DEF
From here on, all manufacturers of high-horsepower diesel engines will use SCR systems with DEF to meet emission regulations. Like it or not, you need to know how to handle DEF properly. Failure to do so can void a manufacturer’s warranty, cause the SCR system to malfunction, cause the engine to shut down, and damage the equipment. Contaminated DEF can also increase your DEF consumption and will be less effective at removing emissions.
DEF is a nitrogen-based solution, so it’s corrosive to most metals and coatings. And DEF is more susceptible to contamination than other fluids.
To ensure that DEF works properly, you want a closed, sealed system so you aren’t introducing contaminants into the fluid. For example, with Thunder Creek Equipment’s fuel trailers, you use a closed-loop coupler (which is the industry standard), hook this up to the source of DEF, and pull DEF from the source into the tank. Then you reverse the flow, put the nozzle on the end of the hose, and push the fluid into the end-use equipment.
Not all new engines incorporate DPFs, but enough do that you need to know the maintenance requirements. The good news is they are pretty low.
Over time, ash from engine lube oil accumulates in the DPF and must be removed by a dealer. For some machines, this will be on an hourly basis and for others it is based on the condition.