CNG CONVERSIONS
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We have had a Crown Vic, two Honda Civics and now a Chevy Cr*palier, all dedicated factory CNG. One difference about the heads may be higher compression, which could also be done with different pistons. Without the HC, mpg and hp goes down about 20%. The reworked valve seats and valves probably have to do with the "dryness" of CNG, even without lead, gasoline, and especially gasoline-ethanol blends have some sulfur and lubricity. Because octane numbers are much higher and energy density so much lower with gaseous fuels, high compression is a must and dual-fuel setups a loser.
People keep equating LPG and CNG. They are quite different. "L" means liquid and "C" means compressed. The 3600psi at which CNG is dispensed creates a lot more safety issues. Tanks, valves, fittings, piping are all much more expensive. Because the tank is inside with passenger car installations, there is also a kevlar blast blanket between the tank and backseat. Is is worth it? It depends. I would never convert, but as we have, bought factory units. The premium for the Honda Civics was about $5k new.
Last edited by jimandmandy; Mar 31, 2011 at 02:58 PM. Reason: Added flame temps for various fuels.
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I read this today regarding natural gas vs gasoline.
Of course there are still hurdles, such as the ridiculous annual fees that the government charges CNG conversion kit manufacturers to have their kits certified; and then there's the preposterous extra restrictions placed on retro-fit conversions by California Air Resources Board, which makes it impossible to convert an existing vehicle or buy a retrofitted vehicle from out-of-state and then registering it in California.
The final rule released by the EPA Wednesday eases regulatory roadblocks to convert older vehicles to alternative fuels. In the case of natural gas this would make it easier for automobile owners and auto shops to legally convert vehicles to CNG as long as they comply with emissions standards.
Just curious why the head honchos at Exxon spent OVER $50B for the largest natural gas concern in America? Hmm. Maybe their mind set is US motorists will be using one of their 2 energy products (gasoline and/or natural gas) in the future?
Also the Federal Gov is looking into tax credits to offset the current price ($4,500) for in-house natural gas fillup systems. It takes about 8 hours to refill an empty tank but all is done within the confines of one's residence. Getting interesting IMHO.
I think conversion kit mfr's and installers to need to be tightly regulated. The hazards of 3000psi need to be taken seriously. We had a CNG Econoline airport shuttle van blow up a few years ago. A flaw was found in the used tank that was part of the conversion. This is NOT a shadetree mechanic job like vegetable oil diesel conversions or even LPG.
CARB is ridiculous in requiring everything to be bone stock, even if it exceeds standards on the tailpipe sniffer test.
We tried "Phil", the in-house refilling station. Its not worth the effort. By the time you buy it, get permits, install and pay for the electricity to run it, the savings evaporate. Filling from a commercial public pump is as fast and easy as filling a gasoline car.
A typical CNG Injection Conversion runs about $6000-$7000. Aftermarket CNG conversions do not require any special engine components other than the engine should be in good mechanical condition. Engines running on unleaded gasoline already have hardened valve seats but upgrades during a rebuild never hurt. Tuning the PCM to optimize timing for CNG would help but would also be considered tampering. There are also special CNG O2 sensors that are more responsive to CNG.
Last edited by fraso; Apr 1, 2011 at 12:41 PM. Reason: added link
A typical CNG Injection Conversion runs about $6000-$7000. Aftermarket CNG conversions do not require any special engine components other than the engine should be in good mechanical condition. Engines running on unleaded gasoline already have hardened valve seats but upgrades during a rebuild never hurt. Tuning the PCM to optimize timing for CNG would help but would also be considered tampering. There are also special CNG O2 sensors that are more responsive to CNG.
New EPA regulations have recently been released and EPA-certified conversions are only available for new vehicles. Older vehicles (older than 2 years) are out-of-luck.
EPA Regulations aren't very clear but there has been discussions on CNGchat that seem to indicate that a CNG conversion is legal if it doesn't tamper with existing emission controls and if the tailpipe emissions are not dirtier.
Most everyone wants to convert for $avings, not necessarily to be "green". Thats merely a side benefit. So, unless the conversion is done perfectly and the parts and installation are durable enough to last the life of the vehicle, emissions could go up compared to the gasoline-powered starting point. Also, safety seems to get little or no mention. At 3600psi, it had better.
As for geography, ArtsBest did not specify his location. It could be CA or it could be OK although his report of $1.93/GGE suggests another state. Many states only have OBD and tailpipe testing and do not look for EPA certificates at annual emission testing.
It is true that the retail price of propane is often higher than the price of gasoline, even in non-GGE terms. However, it is possible to get a good price for propane with a little planning. Since I live just across the river from Buffalo, NY, I called up the local manager of Ferrell Gas. He told me that that the current (winter) price of propane motor fuel is $2.35/gallon with an account. For a motor fuel account, he would expect you to buy their minimum quantity break of propane, which is 1000-5000 gallons per year. 900 gallons/year would also likely qualify as well. If you drive 50 weeks out of a year and had a 20 mpg propane vehicle that racked up 400 miles/week, you would go through 1000 gallons/year. Similarly, you would only have to drive 320 miles/week with a 16 mpg vehicle to also reach 1000 gallons/year. I expect other propane suppliers (like Amerigas, etc) would offer similar deals.
However, it makes more sense to lock-in your propane cost during the summer when the propane market is low. If you did that last summer, you would be paying $1.95/gallon right now in Buffalo. If you add in the sales and road taxes and deduct the $0.50/gallon federal propane tax credit, your net price for fuel would have been $1.7635/gallon. In terms of gasoline energy, that net price of propane works out to about $2.38/GGE. In any case, if you're not buying a lot of fuel, the economics of a conversion will generally not work for you.
As for EPA certification, that has nothing to do with safety as it is purely the ability of the alternative fuel system to meet emission requirements. All certified systems start off as uncertified, universal injection systems. Safety is regulated by NFPA 52 (natural gas) and NFPA 58 (propane) or similar state regulations. Mainstream aftermarket systems (Impco, Prins, Technocarb, etc) meet NFPA safety requirements.
With modern injection conversions, systems are configured so that the fuel trims on propane or natural gas are the same as they would be on gasoline. When the system is correctly set up, injection conversions typically have better emissions on the alternative fuel. It is entirely possible for uncertified system to be as clean as (and as durable as) a certified system.
If you have a public CNG station (run by a gas utility) along your commute, CNG will generally be a lot cheaper than propane in terms of energy and, even though the conversion cost is higher, will generally have a faster payback. I was just checking the price of residential natural gas in Chicago and it's going for $0.4720/therm (monthly basis, HHV), which translates to ~$0.60/GGE. If you had to put it in your own CNG VRA (not cheap) and added in $1.00 for O&M and deducted $0.317/GGE tax credit, your price for motor fuel would work out to $1.28/GGE. The NFGC CNG station in Buffalo is selling CNG at $1.28/GGE today.
Last edited by fraso; Apr 5, 2011 at 11:04 AM. Reason: HHV correction






