Advances in Alternative Fuels for Sweeping

by Allan Heydorn
Created: January 19, 2009

Advances in technology mean CNG and LP fuels can power sweepers ? at a cost.

Filling a sweeper with compressed natural gas can be a little slow, and it can take all night to fill up a sweeper at a slow fill station. Some of the bigger fleets, such as those operated by Los...
Filling a sweeper with compressed natural gas can be a little slow, and it can take all night to fill up a sweeper at a slow fill station. Some of the bigger fleets, such as those operated by Los Angeles, rely on a fast-fill station where large tanks are already filled with pre-compressed natural gas, so operators simply fill sweepers from the one big tank; they don't have to compress the gas first.
Computer controls on engines make natural gas a viable motor fuel because you can hold the mixture exactly where you need it and a computer can make necessary adjustments much faster than an...
Computer controls on engines make natural gas a viable motor fuel because you can hold the mixture exactly where you need it and a computer can make necessary adjustments much faster than an operator can do it.
Initially, operators couldn't put enough fuel in the tanks to make an alternative fueled sweeper worthwhile, but advances in high pressure tank technology now enable larger tanks of various sizes...
Initially, operators couldn't put enough fuel in the tanks to make an alternative fueled sweeper worthwhile, but advances in high pressure tank technology now enable larger tanks of various sizes. So operators can now carry CNG equivalent to the amount the unit would carry if it were a diesel machine.

Manufacturers say they have seen increased interest in alternative fueled vehicles. Initially use of alternative fueled sweepers was driven by a desire to control or reduce emissions from municipal fleets. Giles and Rokas say that both propane and CNG have a smaller carbon footprint than diesel fuel and produce no smoke, soot, and less noise. Then came the rising cost of diesel, which a couple years ago was $1.70 a gallon and last summer was $4 a gallon, and sweepers powered by alternative fuels attracted more attention.

The market develops

One stumbling block that slowed the development of alternative fueled sweepers was that for some time the interest was confined to California. With such a limited market most sweeper manufactures opted not to spend the time and money developing alternative fueled vehicles.

But that's not the only reason development was slowed. Technology had to develop to meet expectations, and today many of these technological problems have been overcome.

CNG, for example, is not as easy to burn as diesel fuel, and the same is true for propane, although to a lesser extent. "A clump of CNG outside in the air won't ignite in the air, and as it spreads out it passes through its burnable point so fast it won't burn then either. It just dissipates," Giles says. "You have to have the exact right proportion of gas and oxygen or the fire will just go out."

Years ago when manufacturers had to rely on a carburetor, adjusting it with screws to come up with the proper mixture, it was virtually impossible to maintain the proper mixture. It was not until the advent of computer-controlled engines that it really became feasible," Giles says.

Another problem overcome by technology is the size of the fuel storage tanks on sweepers. An old CNG tank would hold a maximum of 1,000 psi of gas, severely restricting the distance a sweeper could cover before it had to return to refuel. Advances in high pressure-tank technology enable manufacturers to offer tanks in a variety of sizes and configurations, so new tanks can hold as much as 3,600 psi - enabling the sweeper to operate over a longer range before having to return to the shop to refill. That means more lane miles (or more parking lots) swept, which means more efficiency and greater productivity.

But despite the fact that technology has made alternative fuels more viable for sweepers, the cost of an alternative fueled sweeper is driven sky high because few trucks are designed as CNG or propane-powered vehicles and must be modified as a CNG- or propane-fueled truck.

Future of alternative fuels

Rokas says he expects continued growth in the sales of alternative fueled vehicles, both to public agencies and to contractors, provided there is continued support from the infrastructure to emphasize use of alternative fuels. He says requirements by cities or regions that alternative fuels be used will help grow the market, adding that programs assisting the end user with funding to offset the increased cost - and even federal tax credits - can bring alternative fueled sweepers within reach of many buyers.

"What is driving what looks to be increased interest in these vehicles is the broader emphasis on environmentally sound technology, and that part of the equation is not likely to go away," Giles says. "The other element driving interest is fuel costs, and the fuel side of the equation could dry up in 30 days if diesel prices fall."

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