Interim Tier 4 and Tier 4 Technologies

WorkSaver� magazine continues its series on emission standards with this summary of emerging technologies. This is a comprehensive list of the available technologies to reach interim T4/Tier 4 compliance.

Tier 4

Engine manufacturers identified the fuel injection system as a major focus point to help meet the EPA non-road diesel engine emission levels for iT4/Tier 4. Fuel injection systems affect the diesel engine's fuel consumption, torque, noise and emission levels.

High-Pressure Common- Rail Fuel System (HPCR)

The fuel injection system is a major area of focus for advancement toward clean-operating diesel engines. HPCR is an advanced fuel-injection design that regulates fuel pressure and injection timing.

Fuel Pressure

The pump applies high pressure to fuel (22,000 to 34,000 psi).
The common rail stores pressurized fuel.
The injectors deliver fuel to the engine.

Injection Timing

The electronic control unit (ECU) precisely controls each injector to allow multiple fuel injections during each combustion cycle.

HPCR Benefits

High pressure transforms fuel into an extremely fine mist as it leaves the injectors. Fuel mist combusts (burns) more thoroughly.

Cleaner exhaust:

When fuel combusts more thoroughly, less of it is left over in the exhaust after combustion. The result is cleaner exhaust.

When fuel is injected multiple times during each combustion cycle, the combustion lasts longer to create more energy and lower peak engine cylinder pressure.

Better performance:

Creating more energy during combustion results in more torque output from the engine.

More operator comfort:

Lower peak engine cylinder pressure reduces engine noise levels.

After-Treatment Systems

The good news for non-road engine manufacturers is this: Car and light-duty truck manufacturers complied with EPA regulations years earlier and developed technologies that are now being used on non-road engines. These after-treatment systems take the diesel engine exhaust that has already been created by the engine and clean it further by using one or a combination of the following:

Catalytic oxidation
Heat
Filtering
Diesel exhaust fluid (DEF)

Treatment Systems

These after-treatment devices use filtering, heat and catalytic oxidation to lower emissions in diesel engine exhaust. They're commonly combined with one another in a single canister. Together they lower many emissions but, most importantly, they reduce particulate matter.

DOC/DPF Systems

The diesel oxidation catalysts (DOC) Engine exhaust is transformed by the DOC to reduce particulate matter. The DOC is a special catalyst that reacts with engine exhaust upon contact. The reaction transforms particulate matter emissions in the exhaust into harmless substances such as water and carbon dioxide. See Fig. 1. The diesel particulate filter (DPF) Engine exhaust is filtered by the DPF to reduce particulate matter. The DPF is a special ceramic wall fl ow filtration system that further separates particulate matter from the engine exhaust. See Fig. 2.

DPF regeneration

To keep the DPF clean and working efficiently, the high temperature of the exhaust itself is used to remove accumulated particulate matter from the DPF. This DPF cleaning process is called regeneration. See Fig. 3.

Selective catalyst reduction (SCR)

Engine exhaust is transformed by SCR to reduce nitrogen oxides (NOx). SCR uses an ammonia- and water-based liquid called diesel exhaust fluid (DEF). Combining exhaust with DEF causes it to react with a SCR catalyst. This reaction turns harmful NOx into harmless nitrogen and water vapor. See Fig. 4.

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