Running Generator Under Loaded

[mbrooke]

Does anyone know if there is any negative outcome in running reciprocating natural gas generators under loaded? I know diesel units will wet stack and fail very premature however I can't find anything regarding natural gas units.

 

[drcampbell]

Spark-ignited engines throttle the incoming air, maintain a fairly consistent air:fuel ratio and combustion temperature whether lightly or heavily loaded and aren't likely to suffer any significant problems from running at low power settings. (almost every automobile engine does that almost every day)

It's also much less of a problem for modern Diesel engines with high-pressure common-rail injection and digital closed-loop-feedback control than it was in the past. Don't fall into the "Did you learn that from your dad?" trap.

 

[mbrooke]

Spark-ignited engines throttle the incoming air, maintain a fairly consistent air:fuel ratio and combustion temperature whether lightly or heavily loaded and aren't likely to suffer any significant problems from running at low power settings. (almost every automobile engine does that almost every day)

It's also much less of a problem for modern Diesel engines with high-pressure common-rail injection and digital closed-loop-feedback control than it was in the past. Don't fall into the "Did you learn that from your dad?" trap.

Well, when a hospital's generator room goes up in flames during a hurricane due to known wet stacking it goes well past having learned anything from dad. Scares you enough to consider the issue at every possible opportunity.

Its good to know spark ignited engines aren't susceptible.

Its easy to size a diesel unit to run near 80% load when supplying life safety loads, but a gas unit running a whole building will have seasonal loading. Add 50/50 loading for the loss of one unit and 5-20% loading for weeks on end is realistic.

 

[drcampbell]

I didn't mean to suggest that we should never learn from the past, only that we shouldn't let ourselves be trapped by it, or make decisions based on circumstances that no longer exist.
(full disclosure: I don't know whether the possibility of wet stacking -- unburned fuel (or fragments of fuel such as coke or tar) accumulating in the exhaust systems of Diesel engines -- has been completely eliminated)

Ever listen to Click & Clack on the radio? They made "Did you learn that from your dad?" infamous.
One example: A guy liked to sit in the car and listen to the radio while waiting. (with the engine off) His wife told him he shouldn't do that because it will burn out the ignition points. (they had a model-year-2005 car)

 

[Todd0x1]

It's also much less of a problem for modern Diesel engines with high-pressure common-rail injection and digital closed-loop-feedback control than it was in the past. Don't fall into the "Did you learn that from your dad?" trap.

Tier 4 diesel engines have all sorts of problems running at light load. Its so bad that many of the rental generators now have this stupid looking top hat thing thats a load bank which switches on when the unit is lightly loaded.

A little over a week ago I had a 125kw portable unit from a manufacturer of large yellow heavy equipment loaded with ~50kw overnight, temperature outside was in the low 40s and the thing randomly threw a SCR error and shut down. Fortunately after doing a cold boot restart it came back and stayed on for the rest of the job.

 

[mbrooke]

Tier 4 diesel engines have all sorts of problems running at light load. Its so bad that many of the rental generators now have this stupid looking top hat thing thats a load bank which switches on when the unit is lightly loaded.

A little over a week ago I had a 125kw portable unit from a manufacturer of large yellow heavy equipment loaded with ~50kw overnight, temperature outside was in the low 40s and the thing randomly threw a SCR error and shut down. Fortunately after doing a cold boot restart it came back and stayed on for the rest of the job.

SCR?

 

[mbrooke]

I didn't mean to suggest that we should never learn from the past, only that we shouldn't let ourselves be trapped by it, or make decisions based on circumstances that no longer exist.
(full disclosure: I don't know whether the possibility of wet stacking -- unburned fuel (or fragments of fuel such as coke or tar) accumulating in the exhaust systems of Diesel engines -- has been completely eliminated)

Ever listen to Click & Clack on the radio? They made "Did you learn that from your dad?" infamous.
One example: A guy liked to sit in the car and listen to the radio while waiting. (with the engine off) His wife told him he shouldn't do that because it will burn out the ignition points. (they had a model-year-2005 car)

I know I'm just somewhat skeptical that modern diesel engines can run lightly loaded. I still hear accounts of wet stacking and other problems associated with under loading.

 

[Todd0x1]

SCR?

Selective catalytic reduction

Selective Catalytic Reduction (SCR) | Engine Technology Forum

Learn more about Selective Catalytic Reduction (SCR), an advanced active emissions control technology system that reduces tailpipe emissions of nitrogen oxides.

www.dieselforum.org

 

[mbrooke]

Selective catalytic reduction

Selective Catalytic Reduction (SCR) | Engine Technology Forum

Learn more about Selective Catalytic Reduction (SCR), an advanced active emissions control technology system that reduces tailpipe emissions of nitrogen oxides.

www.dieselforum.org

Thanks

 

[mbrooke]

Reading another thread it sounds like you need to warm up the engine black even on a gas unit?

 

[drcampbell]

Apples & oranges.

Spark-ignited engines throttle the incoming air so there's just enough air to consume all the fuel. Consequently, the combustion temperature and exhaust-gas temperature are more-or-less the same, whether the engine's lightly or heavily loaded.

Diesel engines don't. The incoming air isn't throttled when lightly loaded, to assure that there's enough heat of compression to raise the cylinder temperature above the fuel's autoignition temperature. Then just a wee little bit of fuel is injected, the air and combustion gasses in the cylinder expand and cool, and by the time the exhaust valve opens, the temperature may be too low to prevent water vapor from condensing, too low to keep the catalyst active, and/or too low to keep fuel byproducts from coalescing on the inside of the exhaust system. ("wet stacking")

So much excess air is pumped through an idling Diesel engine's cylinders that it's often unable to keep itself warm in the winter. A block heater won't have any effect on that; its purpose is to make the engine easier to start.