Today, many generators are being factory equipped or retrofitted with Diesel Particulate Filters (DPFs) to meet current emission regulations or bring existing diesel engines into regulatory compliance. A DPF is a filtration system designed to reduce particulate, carbon monoxide and hydrocarbon emissions. A series of alternately blocked channels forces the exhaust gas to flow through the channel walls, where the particulates are physically captured in the filter. The catalytic coating on the filter also converts carbon monoxide and hydrocarbons into carbon dioxide and water. As the particulates are trapped in the filter, backpressure on the engine will rise. Since too much backpressure could cause problems with the performance of the engine, the particulates must be removed through a regeneration of the filter. Backpressure for a catalyzed diesel particulate filter is reduced through a process called passive regeneration. The trapped particulate will start to oxidize (burn off) into CO2 and water at temperatures above 575 F, these gases can then pass through the filter thereby reducing backpressure. With the addition of a DPF and added backpressure, the way we maintain and operate the generator may need to be changed.

Stand by generators get most of their run time during maintenance and testing in preparation for a power outage. During this low load run time, a DPF will accumulate particulate matter due to low temperatures and backpressure on the engine will rise. After 2-4 hours of overall “low-load” run time the filter will need to regenerate (self-clean). The only way to cause regeneration is to build heat in the exhaust, usually above 575 F° at the filter. Complete regeneration may take up to an hour and the only way to build heat is through load on the engine. Even during a power outage, a generator may not have enough load to cause regeneration. A permanently installed automatic load bank may be required for generators that need to have extended low or no load run time. 

Generators equipped with a DPF should have some kind of diagnostic module to monitor exhaust temperature, backpressure, time and date. These monitoring devices will let you know when the filter needs be regenerated. The data from the monitoring device should be looked at periodically and after any power outage.

When testing a generator equipped with a DPF, keep no load run time to a minimum. Most DPF manufacturers will size their filter to allow 12 to 24, 10-minute cold starts prior to needing regeneration. When performing your annual load testing, keep the load high enough to cause regeneration. The typical load steps of 25% and 50% will not only cause the DPF not to regenerate, but most engines produce the highest amount of particulate at or below 50% load. Monitoring the back pressure during the load test will show you the exact point when your particular filter starts to regenerate.

For more information on diesel particulate filters and emission solutions, speak to our Emissions Specialist Daniel Serrano at 800-963-6446.