What if you could get a motor with nearly all of the characteristics of a 4-stroke and the lightweight and power of a 2-stroke rolled into one? Eyvind Boyesen may just be onto something with his revolutionary design.
Ski-Doo introduced the E-TEC motor this year with direct injection and very low emissions while keeping the power and responsiveness, plus increasing the fuel efficiency. Ski-Doo, using the acquired direct injection from their outboard division, accomplished this task using electronics and computer chips. Boyesen, on the other hand, has built prototype engines that accomplish this using mechanical means and the old-fashioned carburetor.
We talked with Joe Nocentino at Hay Days and he was eager to share the Boyesen engine with us. At first we weren’t sure what we were looking at; after all we’ve seen a lot of engines and prototypes that never seem to make it to the market. However, Joe assured us that this prototype is being developed along with a University and a manufacturer and it could show up in future sleds, as well as in Asia, where 2-stroke engines are more of the norm in most transportation.
There’s no denying that 2-stroke engines have a few advantages over 4-strokes; some being lighter weight, more compactness and a power stroke on every cycle. Where the 2-stroke falls short is longevity, efficiency, and emissions. These are changing with the advent of the E-TEC from Ski-Doo to be sure, but Boyesen has developed a system that increases the efficiency and decreases the emissions, similar to that of a 4-stroke.
2-Stroke Basics
We’re all familiar with the exhaust valve on a modern 2-stroke motor. This valve acts to raise or lower the exhaust port depending upon the RPMs of the engine to get the most power it can. This shuts off the exiting fuel charge so that fuel charges will combust more completely. The valves work in combination with a tuned exhaust pipe, which sends a sound wave back toward the ports to push unburned fuel back into the cylinder. If the timing of the valves or the pipe isn’t tuned with the motor or any of its modifications, the power is off, efficiency is low and emissions are high. The charge of fuel that is pushed back into the cylinder is also mixed with spent fuel, degrading some of the power that could be achieved with a fresh charge. Basically it would be like breathing fresh air, but mixing the exhaled air with it, and breathing it in again. Yes, we’ve all done it, but don’t your lungs feel better breathing fresh clean air?
With the E-Tec motor, the fuel charge and air charge are more controlled, and the tuned pipe and exhaust valves all work in sync to provide the most efficient power/emissions/economy combination. A carbureted motor doesn’t’ have the same advantage as an EFI or Direct Injected motor. But Boyesen may have solved part of the equation with a low-cost solution that can be used in conjunction with a carb and without the need for a tuned pipe.
4-Stroke Basics
A 4-stroke engine powers every 4th cycle taking in a charge of fuel and air on the first, compressing it on the second, expanding gas pushes the piston downward on the third and the piston pushed the exhaust out on the fourth. This system allows the use of a straight tube exhaust, catalytic converter and muffler without the need for a tuned pipe. The fresh fuel/air mixture also does not mix with spent fuel giving the motor a fresh clean charge every time.
Well, imagine a 2-stroke engine with ability to cut off the exhaust and go straight to an exhaust tube to a catalytic converter then out to a muffler without having a large bellows of a tuned pipe. It would be similar to adding an exhaust valve (like a 4-stroke exhaust valve, not like the RAVE valves on a current 2-stroke) to a 2-stroke engine, and that’s what Eyvind Boyesen has done with his prototype.
Charge Trapping
The Boyesen design basically traps the fuel/air charge in the cylinder without the need for a sound wave to push it back in. This eliminates the mixing of a fresh charge with a spent charge and Joe told us it reduces emissions and makes more power. The photos we took of the prototype show us a little how it works. An exhaust valve is linked to the crankshaft on a cam system. It raises and lowers the valve to block the charge from escaping, allowing the cylinder to compress the most fuel and air as possible. Then as the fuel combusts, the valve opens with the cylinder to let the exhaust out.
Joe told us that it works great at lower RPMs, but isn’t as efficient as it could be at higher RPMs. Boyesen has plans to make this system a two-stage system to work at peak performance at all RPMs. The photos below show how the system works and quite frankly, we are excited about the technology.
While some companies specialize in 4-strokes, others don’t have the same engineering or means and still require a 2-stroke engine, namely Asian countries where emissions are becoming a huge concern (to the rest of the World, anyway). The Boyesen CT engine may just charge life back into the 2-stroke motor for the next century.
