Beginning in 2008, tier 4 engines were mandated for all new off-road construction vehicles, which includes generators. These high-efficiency diesel engines achieve very low emissions with the help of advanced systems that reduce combustion temperature and trap particulates to reduce the output of pollutants.

Key subsystems of these engines include:

• Diesel particulate filters (DPF) that trap soot and ash in the exhaust system. A substrate usually made of a ceramic material, formed into a honeycomb structure, does the work to capture the particulate matter. In order for this filter to work as designed, the excess soot deposited in the filter must be burned off periodically.
• Selective Catalytic Reduction (SCR) involves injecting a solution of urea and water called diesel exhaust fluid (DEF) into the exhaust stream to reduce engine pollutant output. It turns NOx gasses into nitrogen and water.
• Exhaust gas recirculation (EGR) works to lower the combustion temperature in the engine, therefore reducing the amount of fuel consumed and CO2 produced. It works by routing exhaust gas back into the engine, mixed with fresh intake air. These systems are comprised of an EGR valve that determines the amount of exhaust gas to recirculate, regulating throttles, sensors, and coolers that reduce the temperature of the exhaust gas, further reducing the combustion temperature.

Tier 4 engines have been proven to dramatically reduce the amount of NOx in diesel engine emissions, helping achieve aggressive air quality improvement goals the strict regulations were designed to accomplish.

Problems That Arise with Tier 4 Engines

Naturally, with the introduction of advanced technologies, new challenges arise. These state-of-the-art emissions control features work smoothly when engines are operated under sufficient load and undergo regular preventative maintenance.

But when they are run under a light load, like a standby generator that is only exercised periodically, several issues are likely to develop:

• Particulates that would normally burn off clog the DPF
• DEF that is injected to assist with decreasing pollutants doesn’t bind with exhaust (because there isn’t a consistent flow of it) then crystallizes in the exhaust system
• When the EGR system asks for more fuel, it is provided but clogs because it is not burned off sufficiently

Problems are Difficult to Diagnose

These issues are particularly frustrating to diagnose and solve because their presence generates generic alarms that do not directly point to the underlying problems. If a technician suspects clogging or other issues related to the emission reduction systems, components must be removed, disassembled, inspected, and manually cleaned. 

Recently, due to supply chain problems, we’ve also found that tools required to service tier 4 engines are back ordered or hard to find. 

What You Should Do

In order to avoid costly repairs and downtime, stick to a well-planned preventative generator maintenance routine, including periodic load-bank testing. By running the generator under a sufficient load the engine and emissions systems can generate sufficient heat to clear buildup as well as verify they are capable of generating the power you need.