Say au revoir to the 2-stroke engine - at least as far as Chlysler Corp. is concerned.
Engineers at the company's stroke engine "skunkworks" will suspend further development of the 2-stroke engine, work which began nearly a decade ago under the auspices of Chrysler's highly touted "Liberty" advanced small-car program.
Floyd Allen, Chrysler executive engineer-core and minivan powertrain, announces that the company's 7-year effort to develop a direct-injected (DI) gasoline 2-stroke engine is being shelved and that the AETF (advanced engine task force) housed in Chrysler's Livonia, MI, skunkworks will be assigned to other work.
Chrysler's AETF has been working since 1988 to develop a viable 2-stroke internal combustion gasoline engine, a design which boasts relatively compact size and high power in a package roughly two-thirds the size and weight of a conventional 4-stroke engine. But ever-tightening emissions regulations have reined-in the 2-stroke's potential, making further development unproductive, says Mr. Allen.
The Chrysler 2-stroke had progressed through three iterations, the latest being a 1.5 3-cyl., balance shaft-equipped version that produces 95 hp and 128 ft.-lb. (174 Nm) of torque at 2,400 rpm. - while weighing 80 lbs. (36 kg) less than Chrysler's 2L SOHC 4-cyl. 4-stroke production engine. All of Chrysler's 2-stroke designs feature a wet sump and common "plain" bearings. Gases are scavenged by an external supercharger and the engine employs two spark plugs per cylinder.
AETF was directed until his death in January 1995 by Joe Goulart - almost a legend in 2-stroke circles. But AETF found difficulties in meeting future oxides of nitrogen (NOx) emissions standards with the ported 2-stroke engine. As with any "lean-burn" internal combustion engine, NOx emissions levels are relatively high in relation to engines burning stratified-charge mixtures that typically operate at stoichiometric air-fuel ratios.
Mr. Allen says that if catalyst suppliers can produce a new catalyst able to process lean-burn NOx emissions, the company may again consider further research of 2-strokes. But he says development of the so-called "lean-NOx" catalyst could be five years or more in coming, so unless future emissions standards are reconfigured potential adoption of the 2-stroke will have to "wait for the required catalyst technology."
"Mechanically, it (the current 2-stroke engine) is production-feasible," says Mr. Allen, noting the 2-stroke's high torque output of 128 ft.-lbs. and fuel economy 10% better than a comparable 4-stroke engine. But he admits that in today's market - where fuel economy holds scant priority - the 2-stroke is "not a sufficient breakthrough to displace the current 4-cyl. (4-stroke) engine."
But the years of 2-stroke development have not been fruitless, say AETF members. The 2-stroke program has produced more efficient fuel injectors, a high-pressure fuel pump and a highly developed DI system that will be employed to increase the efficiency and power of new and existing 4-stroke engines (20% to 30% better mpg, says Mr. Allen). Automakers such as Toyota Motor Corp. and Mitsubishi Motor Co. Ltd. recently announced they would begin production of gasoline engines with direct fuel injection, and Mr. Allen says development of direct injection under Chrysler's AETF 2-stroke program allowed the company to cut 18 months or more from its "learning curve" to apply direct DI to 4-stroke engines. Makers of engines for off-road purposes, such as marine engines and powerplants for all-terrain vehicles, also are moving toward DI technology to help those applications meet their own newly adopted emissions regulations.
Mr. Allen also points with pride to an AETF-designed mechanically driven, speed-increasing centrifugal supercharger - also originally designed for the 2-stroke - that may be used on 4-stroke engines as well. The 16:1 ratio centrifugal unit costs considerably less than the traditional Roots-type supercharger, but works best at higher engine speeds.
Interestingly, Chrysler has shelved its gasoline 2-stroke development effort coincidental with growing interest in 2-stroke diesel technology - which benefits from new high-speed, common-rail fuel-injection systems.
Chrysler offers no hint whether a shift to diesel might be in the thinking or planning stage, although a number of powertrain engineers believe it should be part of the AETF's future strategy.
"It's a shame to see it (the 2-stroke engine) shelved," laments one former AETF team member on hand for the 2-stroke's "farewell" demonstration. "It started out as an engine people said wouldn't even run and progressed, in not all that many years, into a very good, refined engine."
"We have no intention of `turning out the lights' on 2-stroke activity," admonishes Mr. Allen. He says that "market forces or market opportunity" - and the development of the required catalyst - will dictate when the 2-stroke engine is adopted for production vehicles.
