Here is the latest reader Q, along with my reply!
First I love your articles. I’ve learned a lot. Now my question. What is your take on propane injection systems for diesels? I know that Australia has been promoting their use for a couple of decades and from what I can gather they are gaining popularity here in the US. I knew a guy who installed such a system on his F250. He increased mileage to 21 mpg and supposedly increased hp by upwards of 100 hp.
I realize they are not for everyone and may be more in the purview of the do it yourselfer, but I would still like your opinion.
I haven’t got any personal/direct experience with the use of propane or CNG in a compression-ignition engine, but my main concern would be the use of a fuel (any fuel) in an engine that wasn’t designed for that fuel.
Propane/CNG have different properties (lubricity, volatility; combust differently) than diesel fuel.
Whether the differences are functionally meaningful would be the thing.
You would also, of course, have to modify the fuel system for pressurized gas rather than liquid and that could get pricey.
Emissions might be lower – or different – or worse. But the real problem is that – in the U.S. – it is illegal to modify or tamper with emissions-related components (this includes the fuel system) regardless of the actual effect on tailpipe exhaust emissions.
In other words, such a mod would likely result in the vehicle failing smog check – even if it doesn’t actually emit smog – which renders the vehicle effectively useless since you need to pass smog check in most states to get or renew vehicle registration.
And of course, your warranty would be void.
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