This is Why You Don’t Convert Your Car to CNG


Converting your car to run on an alternative fuel like ethanol or CNG can be a great way to reduce your carbon footprint without sacrificing performance or reliability. Good conversions, however, are expensive and time-consuming. Cheap conversions, however, can be found all over the internet promising DIY-ers “professional” results at bargain-basement prices. You should watch the dash-cam video, above, and ask the two guys in the video what they think of their converted car’s performance.

I hope you know sign language, though. That’s because the two guys seen leaping out of the car about thirty seconds into that video lost their hearing in the blast and, at the time of its posting, had yet to recover it.

So, be careful out there, guys. There are plenty of people who are willing to sell you dirt cheap kits to convert your car to CNG or LPG or ethanol that, for a few hundred dollars, promise “to save you thousands of dollars”. If it were that easy, everyone would do it. And remember my final piece of advice from the last “don’t convert your car” story I wrote: if you absolutely, positively, must convert your car to propane, my advice is as follows: Spend big money. If you don’t have big money, buy a Morgan. If you can’t afford a Morgan, stay the f*** away from eBay.


Convert Your Car to CNG, Go Boom


Source | Images: CarBuzz.

About the Author

I've been in the auto industry 1997, and write for a number of blogs in the IM network. You can also find me on Twitter, at my Volvo fansite, or chasing my kids around Oak Park, IL.
  • Dave Lecture

    Will be interesting to see what kinds of explosions you get from the Toyota Mirai’s dual 10,000 psi hydrogen tanks…

    • As with any flammable gas, it will all be about surface area exposure to oxygen. With that much pressure, you’re more likely to get a long stream of fire that dissipates quickly than you are an explosion.

      In answer to your next question: because the Hindenburg wasn’t pressurized in the same way.

      • PrezNixon

        Having a long stream of fire that dissipates relatively quickly would be one failure mode. That would be what would happen if a hydrogen release immediately started burning as soon as it starts leaking.

        The other mode of failure is that the hydrogen starts leaking into a closed area (like the interior of a car) until it collects in enough concentration that heat, flame, or spark finally sets it off.

        That failure mode gives you the kind of surface area you are talking about, and the kind of explosion that you don’t want to be around.

        Any time you store energy in any form, you face the risk of a rapid release of that energy. That is true for a hydrogen fuel cell, a gas tank, an electric battery, or even a hay stack to power your horse for your buggy.

        The failure mode when that energy is released is what differentiates different fuels. Fuels in a gas form all face the risk of slow leaks leading confined spaces being saturated slowly with fuel until they reach an ignition source and cause a highly oxygenated high energy explosion.

        Volatile liquid fuels face the same problem, plus the risk of the fuel being sprayed and splashed and spread in an accident.

        Semi-solid fuels like batteries can also have this same risk if they off-gas explosive gases (like the GM battery destructive testing explosion, where they were intentionally trying to destroy a battery, and they succeeded much better than they expected…)

        • I don’t think that kind of slow leak is possible with a system as pressurized as a hydrogen fuel cell would necessarily have to be, though.

          • PrezNixon

            10,000 PSI or 20,000 PSI is the MAXIMUM pressure you can fill an H2 system to. This is not to be confused with a constant operating pressure.

            As the H2 is consumed, the pressure drops. H2 fuel tanks operate at a whole range of pressures.

            There is also a pressure difference between the fuel cell storage tank, and the operating pressure inside the fuel cell itself. The fuel cell doesn’t operate a full tank pressure. And a leak from either can both lead to explosions. For some reason everybody fixates on the storage tank, as if it is the only possible point of failure. But it isn’t.

            It would be a mistake to make assumptions about how an H2 system will fail based just upon the maximum pressure in the tank itself. when the tank is full.

      • Joe Viocoe

        It really depends on the velocity of the stream. A very small puncture may lead to a very fast exiting stream.

        But a tear of the structure of the tank, say from an accident… weakens the structure, and may provide a large enough gap area, that Hydrogen pours out slow enough for the fast flame speed of H2 to travel back to the opening, and cause a cascade failure. BOOM!

        Or even without a flame, an accident that sufficiently compromises the tank… 10,000 PSI will blow your car up just fine. Along with the poor passengers in the back seat, who were foolish enough to sit on top of that kind of stored energy. (remember, there only is 5kg of Hydrogen, which is only 170 kwh of energy… but there is also the energy of pressure, if released all at once).

        Never assume things go as planned in a chaotic event like that. I would much rather have a battery, which has physical limits on how fast it can cascade. So far, every EV battery fire has been a slower burn, giving occupants minutes, instead of microseconds.

        • Right, but the pressure in a hydrogen tank is orders of magnitude greater than a DIY propane kit. You won’t get a slow leak- and they seem to be built of sterner stuff, too, preventing the kind of catastrophic tears you’re thinking of.

          That said, even in a worst case scenario, it’s not like gasoline is exactly inert under similar conditions.

          • Joe Viocoe

            When hit by another car, there is no material that can successfully resist tearing.

            And slow leaking is still possible in a number of ways. It really depends on the type of damage.

            Agreed, it may just be as bad as a gasoline vehicle. That isn’t comforting though.

          • My point is: by the time you’re in an accident that tears your fuel tank open, you’re already pretty well boned.

          • Joe Viocoe

            Not necessarily.
            Take what happened to Tesla. Metal road debris at 80 mph tears under the car. The tank under the back seat goes Boom, instead of the slow burn of a battery.

          • Well played. 🙂

  • Jason Willhite

    Are we sure that the car didn’t just have a wicked speaker system and forgot to reinforce the trunk?

    • I … oh, man. I so want that to be true.

      • Jason Willhite

        If it was the sound system exploding, we may have just witnessed one epic bass drop. 🙂

        • Just post the same video with the caption “epic bass drop” and see how many views it gets!

  • The key to this is “experienced technician” and “technical inspection”. In the US, there are a number of companies offering inexpensive kits and marketing them to people as a sort of, “anyone can install this” kit. That’s very dangerous, and it’s why I recommend spending a little extra to get quality parts and a quality installation.

  • Carney3

    CNG is under high pressure and needs a high pressure fuel tank. I don’t see the relevance to converting to ethanol, which is not under pressure and can use a normal fuel tank. In fact ethanol is safer than gasoline because it is harder to ignite, needing a narrower range of fuel to air ratios and a greater input of energy compared to gasoline. So equating CNG conversions to ethanol conversions smacks of FUD.