The Impacts of Running our Fleet Vehicles on Propane

by Mar 3, 2015Mobility, Resources

Hannah Greinetz

Hannah Greinetz holds a BA in Anthropology from UC Santa Cruz and an MBA in Sustainable Management from Presidio Graduate School.

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In my last article, I focused on the seemingly overlooked benefits of using propane as fuel for our vehicles. The merits of propane have been recognized by city governments, propane alliances, and the Department of Energy through its Clean Cities program. And with the current increase in domestic oil supply, comes an increase in domestic propane supply. Yet, relative to oil, there are few uses for propane in this country, even though we’ve got a lot of it and we’ve recognized the benefits of running our most prolific energy user on propane: automobiles.

And if we were going to prove the concept in practice, the natural place to start would be with the heaviest fuel users – the vehicles that get the lowest number of miles per gallon of fuel, have the biggest fuel tanks, refuel most often, and travel in packs – fleet vehicles. Converting fleet vehicles to run on propane has the biggest impact, since they’re doing the heavy lifting. Think about fleet vehicles in cities: they’re performing road maintenance and parks maintenance, fleets include city buses and school buses, as well as police cars and emergency vehicles that can’t afford to operate on low-range electric plug-in options.

If SD converted 5% of its fleet vehicles to run on propane…

The county of San Diego manages a fleet of over 3,800 vehicles performing a variety of services in the city and county. The San Diego regional area is a member of the Clean Cities coalition run by the Department of Energy, which works with vehicle fleets, fuel providers, and community leaders to reduce petroleum use in transportation. It’s feasible to think that San Diego could convert 5% of their fleet vehicles in an effort to directly reduce their dependence on oil and to capture the other benefits of propane as automobile gas. As we learned last month, these benefits include reduced emissions for better air quality, savings on fuel costs, and reduced maintenance costs.

The EPA regulates the process for converting vehicles from gas to propane; more specifically, the EPA issues conversion certificates to authorized dealers who have paid to have their process for conversion seen and permitted by the EPA. The authorization signifies that vehicles converted by the dealer will be in accordance with EPA emissions standards. A certification must be gained by the dealer for each engine family that they wish to work with, and the certificates don’t come cheap. For the county of San Diego, it would make sense to pay a dealer to convert their light duty fleet vehicles, which would come at an upfront cost of around $6,000 per vehicle. The savings on fuel and maintenance costs will offset the upfront investment in converting the 190 vehicles, representing 5% of San Diego’s fleet.

The County Would Save Big

Gas prices have taken a noticeable dip in the past months, however, propane prices have remained lower still. At this time last year, and on average over the past few years, propane prices have been $1.25 – $1.50 cheaper per gallon than gas prices. This savings on fuel is largely where fleet managers recoup the high upfront costs incurred for converting their fleets’ gas engines to run on propane. The latest data on fuel prices, for the week of February 23, puts the national average price of gas at $2.42, and the national average price of propane at $2.36.

So, even with lower than average gas prices and assuming they stay this low all year, if San Diego were to convert 5% of their 3,800 fleet vehicles to run on propane, and assuming the average fuel economy of a US light duty fleet vehicle is 17.1 mpg, and the average light duty city fleet vehicle travels 14,536 miles per year, San Diego would save $9,690 on fuel costs alone this year.

In a ‘normal’ year, with fuel prices at an average of $1.25 more than propane prices, San Diego would be looking at a fuel savings to the tune of $202,000 per year.

Apart from the decrease in fuel costs, maintenance costs are also documented as being cheaper for propane vehicles than for gasoline engines. By some estimates, maintenance costs are reduced by 50% when running an auto engine on propane.

San Diego would be doing its residents a service in converting vehicles to propane through the benefits the public would reap in better air quality. The Ford F-series trucks have been the number one selling light duty vehicle in the US for the past 27 consecutive years, and the GHG emissions numbers below have been calculated based on a Ford F-150 traveling 10,000 miles per year at the 14.7 average mpg. We can see from the table that by converting 5% of their fleet, San Diego would be directly reducing the amount of carbon equivalents (think emissions & particulates) in the air by 1,340 kgs per vehicle per year, which adds up to 254,600 kgs per year, and cleaner air in San Diego.

Not to mention that San Diego’s 190 conversions would directly reduce our nation’s oil consumption by over 161,500 gallons of gas per year. The impacts and implications of running just a small percentage of our vehicles on propane are huge, so the last piece of the puzzle remains – what about the infrastructure? Stay tuned for the final article in this series that will examine the barriers to running and sustaining a propane vehicle economy.


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  1. Your analysis overlooks one very important detail. One gallon of gasoline contains approximately 120,000 btu. One gallon of propane contains approximately 91,000 btu. Since btus are what makes an engine run it can be assumed that if a vehicle gets 20 mpg on gasoline it will only get 15 mpg on propane. The other leak is encountered when converting gasoline engines to propane. Please don’t misunderstand, I believe that propane is a wonderful motor fuel in that it is clean burning relative to gasoline and greatly prolongs engine life for reasons I will not detail here. Propane, however, is a 108 octane motor fuel. This means that in order to function efficiently using propane as a fuel an engine needs to have a compression ratio of around 11 to 1. Most modern gasoline engines designed to use unleaded gasoline have compression ratios of around 7 to 1. This compression ratio using propane fuel causes increased emissions and reduced performance which is not the case with an engine which was specifically designed to use only propane as its fuel. Fleet operators would be well advised to purchase new units specifically designed for propane rather than converting gasoline engines to propane.

    • First, who is Hannah Greinetz and how is that I haven’t heard of her since I’ve been working for the Western Propane Gas Assn on a part-time retainer for many years in CA and have been on the Board of the Greater Sacramento Clean Cities Coalition for several years? Great article (“The Impacts of Running….) written by her, tho’ it will never curry favor with the electric vehicle, hydrogen, and natgas vehicle acolytes who run the CEC, CARB, SCAQMD, and other CA agencies. I’m glad she had the courage to say what she did….

      A note or two with respect to her article and the one commenter’s thoughts:

      The Roush F-150 used for GHG benefit calc’s doesn’t exist in CA–Roush missed the boat by an ocean or two’s distance with their decision to not pursue that vehicle (isn’t it the country’s most popular truck and bestseller?) and especially for CA. Farmers, contractors, school districts and others have all asked the propane world for it, and have generally turned their nose up at the F-250 that I’ve had to loan to them on behalf of the Western Propane Gas Assn. They like the performance…but don’t need the heavier suspension and don’t want to have to pay the substantially higher DMV fees it requires.

      2nd item–fuel prices. UPS has committed to 1000 Autogas delivery trucks, and in my northern CA area there are about 100 operating (or soon will be). I can guarantee you that the price for LPG they’re paying is far below the nat’l avg $2.36/gallon quoted for propane by Hannah. In summer, when gasoline and diesel are at their highest, LPG is at its lowest. Good example of fuel savings is that experienced by farmers pumping summer water with LPG-fueled engines (finally!) instead of diesel, paying less or much less than $1.75 a gallon and saving a dollar a gallon over diesel AFTER you adjust for btu differences. Think the same can’t happen for onroad vehicles? Think again—it’s perfectly possible.

      3rd item—Gerry McEwan’s comments regarding fuel efficiency and engine design. Liquid-injected Roush (and other) Autogas vehicles reduce NOx while taking advantage of the fuel’s higher octane rating—the 24% reduction in btu content of LPG (vs. gasoline) should mean a 24% redux in fuel economy, yet the avg is about 15% with the benefit resulting from highly-refined engine fuel mapping, rate shaping, advanced timing, etc. Call it Roush engineering magic–and if you look at the hp and torque curves for the 6.2L engine on LPG and gasoline, they overlay almost identically. Translation: you get an alt-fueled truck that is virtually transparent in performance to its beloved (by OPEC) gasoline counterpart. And I disagree with the 11:1 compression ratio cited by Gerry—highly controlled modern LPG engines are currently at their limit at about 10:1. Someday, perhaps, Ford and others WILL build vehicle engines optimized for LPG….but the current slate of highly engineered engines with boosted turbos and aftercooling would do nicely on LPG without higher compression ratios if anyone were interested in producing them. Last thought–Roush has retrofit certified with CARB their systems for certain Ford trucks and vans, but otherwise there are virtually no legal, CARB-certified systems for onroad vehicles that will “convert gasoline engines to propane” as Gerry assumes. Bottom line: you want an Autogas vehicle legal for use in CA, you’re virtually certain to buy new.

      Thanks………Greg Gilbert, Autumn Wind Associates

      • Greg,
        Thank you for your thoughtful reply to the article; I appreciate yours and other commenters’ perspectives on the octane ratings in regards to fuel economy, and especially coming from your industry experience. I think our perspectives on the bottom line of the argument come to a consensus around the difficulty you’re citing for those who want propane vehicles, to get access to them and the savings on fuel that they represent. The DMV fees for heavier vehicles, and the EPA fees for certification to convert OEM vehicles to propane seem like the heart of the issue in bringing propane to the table as a viable alternative fuel – one that people have the option to access (through built infrastructure – public filling stations) if they had the information and the desire to run their vehicles on it.
        I appreciate your insight into the prices paid by private fleet users as opposed to the national average fuel prices; those numbers are also what make the case in the end for fleet managers. I was unaware that there are no conversions happening in CA for F-150’s because, yes, those are the most popular fleet vehicles in the country. Just getting a sense of the hoop-jumping that happens around getting vehicles CARB, and CAFE, and CEC, and EPA certified; it’s no huge wonder that there aren’t more players in the this market or in this conversation.

    • I run my FedEx fleet on propane and I only see a 5% MPG loss over the past 3 years. Your data must be outdated. Best decision I’ve ever made is switching to propane dual systems from ICOM. 95% efficient!

      • Wow! Mr. MacDonald’s has been very lucky with his Fleet of converted vehicles. I on the other hand, service a fleet of over 70 Vans converted with the ICOM system, and the only 95% figure here is the time these vehicles are down.I would not recommend converted vehicles for fleet use, In my experience they spend more time down and out of service than on the road. Since these are basically adapted systems, there is little to no diagnostic data available. I would recommend a dedicated system from the manufacturer.

  2. Not sure where Gerry did her research, but modern day engines are typically 9.5 to 1 compression ration, far from her 7 to 1. 10.5 to 1 is the highest compression ration recommended even for CNG. Yes propane has a higher octane, which runs great in a 107 octane engine with a computer that controls the timing. The BTU difference can not be the only factor to determine fuel mileage just based on energy content alone. Fuel mileage differences in the real world are documented by many fleets and average about 12% less. Calculate cost per mile not miles per gallon.

  3. Thank you Hannah for this great propane autogas. Like hundreds of fleets around the country, San Diego county can benefit economically, environmentally and socially by deploying the most preferred alternative fuel in the world. The propane industry greatly appreciates professionals like you who understand our fuel, see the “big picture” and are not afraid to share it with the public.

    Regardless of prevailing opinions and comments, propane autogas has proven time and again to provide fleets with the lowest Total Costs of Ownership when compared to all conventional and alternative fuels. Today’s EFI technology has proven to be a game changer for propane autogas as we are seeing comparable performance without compromising horsepower, torque or towing capabilities when EPA and/or CARB certified OEM and aftermarket fuel systems are deployed. Also, certified aftermarket conversions provide equivalent performance while providing satisfactory results for end users. I would be remiss if I didn’t point out tha certified aftermarket fuel systems account for more than half of all propane autogas sales in the United Sales. From passenger cars to school buses, certified propane autogas OEM and aftermarket fuel systems are getting the job done and saving fleets money. Actual performance results are dramatically affected by the person behind the wheel so it always helps to have good drivers regardless of the fuel.

    With the implementation of CAFE standards and stricter EPA air quality standards, OEM’s are transitioning to Direct Injection (DI) fuel systems to attain the required higher miles per gallon while reducing emissions and not sacrificing engine performance or miles per gallon. This is good news for propane. Testing has proven that propane autogas provides optimal performance in DI engines when compared to gasoline. Propane autogas does not have the carbon buildup issues which have been a nemesis for today’s gasoline engines. And, while science tells us it is not possible, propane autogas DI engines in the real world are moving closer to MPG parity with gasoline engines. The future looks bright for propane autogas.

    Once again, thank you for supporting propane autogas and sharing the facts with your readers. Hopefully, San Diego will be added to our long and growing list of satisfied propane autogas customers thanks to your efforts!

  4. It’s interesting to see the monetary impact of converting fleet vehicles to run on propane. Saving more than 200,000 dollars a year in San Diego is an appealing incentive. But how difficult is the conversion from gas to propane for vehicles? Would there be any additional costs that fleet operators should be aware of?

  5. I like to convert my car to propane here in San Diego.. but I need more info about Propane conversion centers


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