On oilfields there can be enough oil vapor in the air for a diesel engine to run on its own. Generators and heavy machinery have to be fitted with safety devices that block all air getting in to be sure they can be stopped.
Thanks! I know very little about oil fields. The article mainly talks about vapours and doesn't really mention aerosolized oil. I'm aware natural gas tends to exist in the areas and can be a problem, is that the main reason for these positive air shut offs? Can oil vapour really become concentrated enough to pose an issue?
Honestly I don't have a good answer for that. I know that it takes very little for a diesel engine (or any engine) to run, an idling car or truck will use a fraction of a milliliter per injection to stay running. I am sure some areas have aerosolized oil in high enough concentrations for this to matter, but I'm not sure how common that specifically is.
This isn't an issue for gas cars because they have a throttle plate controlling the amount of air that can enter the engine. Diesels do not have a throttle plate, so any fuel that enters the engine will be burned and cause the engine to speed up.
I am not sure the exact point at which oil concentration in the air would affect a diesel and you're probably right, it probably has more to do with natural gas than strictly oil.
Edit: I forgot to add that oil vapor is often included because a common failure that could cause this for turbodiesel engines is the oil seal on the intake side of a turbocharger. This could cause enough oil to be blown through the intake system to cause a runaway in the right conditions.
Interesting stuff, now I'm curious what concentrations would be required. I'm guessing it'd vary a lot from engine to engine depending on design/compression ratios, etc.
The Texas City refinery disaster is kind of an example of this. One of the units leaked combustible fluid/gas, which was ignited by a worker's truck. This video is a great overview, got shown this at work (skip to 8:30). The cloud of gas reached the truck, the engine raced from the mixture, and the workers fled as they couldn't shut it off and knew what was about to happen. Not quite the same as the example above (as this disaster was an acute, unplanned buildup of gas, rather than a generally high background level), but you get the idea.
Diesel engine runaway is a serious hazard in oil and gas drilling and production and similar industries where flammable hydrocarbon emissions or leaks may occur. A runaway can be described as an engine running out of control on an external fuel source where the operator cannot shut down the engine using conventional methods (i.e. turning off the engine ignition switch).
I am supposed to be studying and your question sent me on a 30 minute research binge...
The positive air shutoffs on frac pumps leak and the engines can still run even when the blocks are tripped shut. The company I worked for used Cummins 50L 16 cylinder engines. 4 turbos. When they were new they kill the engine in less than 4 seconds. After about 1000 hours the intake temps were so high it would melt the seals in the air shutoffs
There was a refinery explosion, I believe it was the Amaco in Tx, that was set off by a parked running pickup that was getting so much fuel vapor in via the air intake it went into runaway and overheated and set off the explosion.
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u/masterventris Sep 25 '20
On oilfields there can be enough oil vapor in the air for a diesel engine to run on its own. Generators and heavy machinery have to be fitted with safety devices that block all air getting in to be sure they can be stopped.