Diesel Generator Enclosure - fire proof or blast proof

[ChemEngSquirrel]

I have a diesel genset / diesel engine that will be located in a fire rated enclosure.

Generally, you do not get diesel fires. However, in the diesel engine temperature will be high. Is it possible to get an explosion in the enclosure due to the diesel fuel being ignited by a failure in the engine?

I'm concerned about an explosion in the enclosure damaging adjacent safety critical equipment. If it's a risk then i'll need to specify that the enclosure be blast proof instead of just fire proof.

 

[bimr]

The actual burn temperature or self ignition temperature of diesel oil is around 500 deg F, so it should not ignite. Consider fire proofing the diesel oil tank.

 

[crshears]

Although I can't quote code, chapter or verse, Diesel fuel and the engines that use it are generally considered non-volatile, therefore a fire-rated enclosure should suffice.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[MikeHalloran]

Modern 'common rail' Diesels use super-high injection pressures, such that leaks are capable of generating a very fine mist of fuel that is easy to ignite, e.g. by contact with a hot exhaust manifold. It is enough of a concern that yacht class societies require the presence of double wall injector plumbing, and a leak detector between the walls, set to shut down the engine after a small amount of fuel has leaked from the inner wall. It is an expensive option on marine Diesels. Terrestrial CR engines are not, AFAIK, required to have it, and it may not be available for any given model.

I am not sure what you mean by 'fire rated'. The enclosures with which I am familiar have fire-actuated shutters on all ventilation openings, and an automatically deployed bottle of fire suppressant of some kind. They do not appear sturdy enough to contain much of a blast. ... and, given the open area needed for radiator cooling air and cooling air for the engine itself, the manifold and the muffler, I'm not clear how one might make a 'blast rated' enclosure.

Could you relocate the generator?


Mike Halloran
Pembroke Pines, FL, USA

 

[Hoxton]

I thought that I had posted, but must have gone astray.

I have seen gensets in fire rated enclosures, but it is not common, normally fire / smoke detection and genset trip with fuel shut off is considered adequate.

I have never seen a blast rated diesel genset enclosure, but no doubt I will be corrected! I assume that the ignition of diesel at normal pressures and temperatures do not create sufficient pressure to cause concern. As Mike Halloran says, what would you do about ventilation intake and extract apertures?

If someone has specified a fire rated enclosure, then we can only assume that there is a good reason, and that getting out of it may be difficult.

Any ventilation ductwork, attenuators, shut off louvres etc. may also need to be fire rated.

Leaking fuel at low pressure poses a low risk of fire but as Mike Halloran says, the risk is of a leak from an injector pipe spraying a fine mist onto a heat source, e.g. a turbocharger or exhaust pipe. This applies to conventional diesels as well as common rail systems. In fact the marine industry has gone over to twin wall injector piping since the early 2000’s under SOLAS regulations.

Interestingly, in the UK we do not even fit blast or fire rated enclosures to gas engine packages. With these, a fuel gas leak could result in an explosive mix. This risk is mitigated by gas and fire detection, ventilation design, external fuel shut off etc.

 

[bimr]

The real concern is the location of the fuel which you have not addressed.

 

[gr2vessels]

My two cents;-
1. The fire rating of genset enclosure normally refers to resistance to external fire, not internal. Inside the enclosure is not normally rated as ignition risk, let alone explosion risk.
2. The blast rating of enclosure also refers to external blast, not inside the enclosure.
The proximity of external fire source or explosion require the enclosure to be strengthened up for these cases. The inside environment is protected by fire and gas detectors, so the only real source of ignition (diesel engine) will be immediately shut-down and enclosure air inlet louvres shut to keep out hydrocarbon gases.
BTW, where is potential of enclosure internal ignition of gas, the exhaust manifold is water cooled below any potential ignition temperature. The presence of ignitable gases in enclosure will inhibit the start of the diesel engine by the gas detectors interlocked with engine ECU.
Cheers,
gr2vessels

 

[MikeHalloran]

Until a few years ago, marine Diesels were allowed to be equipped with air cooled exhaust manifolds, covered with fire resistant blankets. Now, water- cooled manifolds are required. Even those glow cherry or orange at the turbo flange at WOT.

AFAIK, terrestrial Diesels are not required to have water cooled exhaust manifolds or water cooled turbos. You can probably get them equipped that way if a corresponding marine model exists, but you'll need to upsize the radiator.

Note also my comment above about CR Diesels, which are virtually required in order to meet emissions regulations, and which provide a very fast moving fuel mist when they develop a leak. They are not your old Jimmy Diesel.




Mike Halloran
Pembroke Pines, FL, USA

 

[FreddyNurk]

I've never seen anyone actually specify blast rated enclosures for diesel engines, I've personally been involved in a somewhat drawn out review of the possibility of explosive atmospheres in a diesel engine enclosure, but the overall consensus at the end was that the possibility of explosion was highly unlikely, even with such possibility as high pressure return fuel line leak at elevated temperatures. In all cases the concern is high pressure atomised diesel mist, either at high temperatures, or within close proximity to exhausts, turbos and so on, rather than wholesale leak of liquid diesel.

That said, I've seen a few cases of diesel generator fires for various reasons, usually its some sort of leak that ignites as it hits the turbo or exhaust manifold. Reasons I could think of for having fire rated enclosures:

There are multiple sets and the spread of fire from one set to another needs to be prevented​

Its better to be able to manage a single engine fire than a whole engine hall full of diesel engines​

Most of this pertains to structural integrity as well as stopping the spread of fire. The last installation I saw that caught fire was a room in a larger building constructed almost entirely of 200mm masonry block, and it ended up needing to be demolished after the fire, although it did stop the fire spread to a certain extent.

Other issues surrounding the installation can be problematic, such as source of diesel (day tanks inside the enclosure can be an issue), shut off and isolation schemes, and the additional cost of any fire suppression scheme that may be needed.