My father asks, can smoke in the air from wild fires cause a fuel injected engine to choke?

(He seems to think this was once true for carbureted engines - was it?)

My personal guess is that we can look at how car engines (still) work on rainy days and at emissions technology like EGR and reason by analogy: a very thick cloud of smoke might somewhat lower the combustion temperature, but not enough to stall the engine, although it might make the emissions or MPG worse. Heated intake air might lower the volumetric efficiency by a small amount, maybe similar to high altitude (and opposite to the effect of a rainy day increasing VE). And particulate matter might clog the air filter, but it would take a long time.

I wouldn't expect a density of smoke that does not already kill the driver to have much effect on either carbureted or FI cars, but perhaps if there is a difference maybe more modern fuel injected could sense and lower EGR to compensate for there already being smoke in the chamber and could lower fuel air ratio to compensate for the hot/dry air.

1 Answer 1


TD DR: You nailed it.

For the amount of CO2 (and/or CO), think about a running car in a garage. If a person is trying to commit suicide, the driver will be dead long before the car quits running due to a lack of oxygen. (EDIT: Just thinking about this, I believe a person is asphyxiated from CO versus a lack of oxygen in these cases ... not sure if that invalidates my theory or not.)

In a forest fire scenario as you suggest, the engine may suffer a little bit by the lack of oxygen, but it would kill the driver well before it would kill the engine. The engine can adjust itself to the amount of oxygen it intakes ... a human cannot.

As you suggest, if there are any large particulate matter in the air, the air filter will get rid of these. If it's smaller than what the air filter can take care of, it will just go into the engine and be pumped through just like it was exhaust being introduced via the EGR valve. It will squelch the combustion process a little bit and the car may be down on power somewhat, but it's not going to kill it.

There may be physical factors which would stop a car in a forest fire, like the heat. The car may catch on fire from the infrared radiation which is produced from the fire itself. Direct fire contact will have devastating consequences as well (obviously).

  • CO, CO2 or noxious gases would be the main killer. Humans can survive on O2 levels non-trivially below normal (c.f. high altitudes), while CO2 and CO are toxic.
    – Demi
    Jun 9, 2017 at 18:02

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