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Two Strokes and You're Out

Impressive new tech reduces pollution from small engines by almost 90 percent.

By David Kushner
May 21, 2008 12:00 AMOct 8, 2019 7:27 PM


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In 2001 Mary Jane Ortega, then mayor of San Fernando City in the Philippines, knew her city was choking to death. The cause? Air pollution, specifically that from two- and three-wheeled vehicles powered by dirty two-stroke engines, including motorcycles, scooters, and the motorized rickshaws known as tuk-tuks.

Around the world, outdoor air pollution kills 800,000 people a year and sickens many more. While big vehicles like Hummers and other SUVs are often blamed for excessive emissions, some of the worst culprits are the smallest rides around. Throughout Asia, vehicles with two-stroke engines produce vast amounts of pollution. “In the cities of many developing countries, the pollution is horrific,” says Daniel Sperling, director of the Institute of Transportation Studies and acting director of the Energy Efficiency Center at the University of California at Davis. “Two-stroke engines are a big part of the problem.”

Unlike the developed nations’ larger but much more efficient auto­mobiles, which use four-stroke engines, two-stroke vehicles spew great volumes of dangerous hydrocarbons, carbon monoxide, and smoke. A single two-stroke engine produces pollution equivalent to that of 30 to 50 four-stroke automobiles. With roughly 100 million motorcycles in Asia—roughly half of them using two-stroke engines—that translates into as much as 2.5 billion cars’ worth of smog. The obvious solution would simply be to get rid of the two-strokes, which Ortega tried by offering economic incentives, including an interest-free $200 loan for a down payment on a new four-stroke-engine vehicle. Within three years, 400 four-stroke engines had replaced two-strokes in San Fernando—but more than 800 registered two-stroke tricycles remained on the city’s streets. Even with a loan, upgrading to a four-stroke vehicle proved too costly for many. Furthermore, the tossed vehicles get sold and reused, merely transferring the pollution somewhere else. What is needed is a cheap solution to those two-stroke engines already in place.

Bryan Willson, director of the Engines and Energy Conversion Laboratory at Colorado State University (CSU) in Fort Collins, has cofounded a start-up, Envirofit, that sells a retrofit kit for two-stroke engines. The technology reduces hydrocarbon emissions by almost 90 percent while increasing fuel efficiency by as much as 35 percent. The first 400 kits were made available in the Philippines last fall. The U.S. Environmental Protection Agency (EPA) awarded Envirofit a contract to retrofit two-stroke auto-rickshaws in Pune, India, and is spending about $100,000 to test the Envirofit kit there this year. “We’re sponsoring a pilot program to see if conversions are a viable technology solution for these vehicles in India,” says Margot Perez-Sullivan, a spokeswoman for the EPA. The goal is to have 15,000 retrofits in Asia by the end of 2008.

The United States is interested in Asia’s two-stroke problem because “pollution knows no boundaries,” Perez-Sullivan says. In America, two-stroke engines are limited to recreational vehicles such as snowmobiles, Jet Skis, and outboard motors. The industry will introduce its own two-stroke direct-injection alternatives this year.

Two-stroke engines produce a lot of pollution because the fuel-air mixture in them gets contaminated with the engine’s lubricating oils. Simultaneously the combustion chamber draws in the contaminated mixture as exhaust gases are expelled through an exhaust port. Some of the fuel and oil gets mixed with the exhaust.

Envirofit’s fix replaces the engine’s carburetor, which mixes the air and fuel before they enter the combustion chamber, with a direct in-cylinder fuel-injection system. This allows fuel to enter the combustion chamber when the exhaust port is closed. Eliminating nearly all the unburned fuel significantly reduces the ensuing smoke and hydrocarbons. The conversion kit includes an air compressor, wiring harness, custom brackets, and a new cylinder head.

Envirofit developed the technology somewhat by accident. In 2002 a group of Willson’s students entered a contest sponsored by the Society of Automotive Engineers; the goal was to develop a clean snowmobile engine for use in Yellowstone National Park. The team built a two-stroke snowmobile that won the competition and sparked a business idea.

In 2005 Envirofit field-tested the retrofit kit on 13 tricycle taxis with sidecars in the Philippines, which had struggled with emissions problems for years. After eight months, the results were impressive. Not only did the kits cut back emissions, but they saved taxi drivers money and enticed them to get on board. Glenn A. Concepcion, city environment and natural resources officer in Vigan, the Philippines, says the people in his city were initially skeptical of the kits. “But now, this is diminishing with the convincing results of the field test and the actual experiences of the tricycle drivers in the field sharing those experiences with other drivers,” Concepcion says.

Saving money is critical to persuading these drivers. “It’s not like a New York City cab company,” says former CSU student and Envirofit cofounder Tim Bauer. “These two-strokes are owned by one person making $1,500 a year. You have to make them understand it will make them more money,” which it does, Bauer says. By cutting fuel loss and reducing oil use by up to 50 percent, the modified engines may save their users as much as $600 a year. Bauer believes that Envirofit could produce up to 500,000 kits in five years, “putting $190 million into the hands of some of the poorest people” in the world.

“After six months of using the Envirofit retrofit kit, my extra income helped me save for a matching house grant,” says Rolando Santiago, president of the Tricycle Operators and Drivers Association, in the Philippines, and among the first to retrofit his bike. “I rebuilt my home and my neighbor’s home, which provided housing for six families,” he says—proof that better air can lead to a lot of other better things.

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