In order to better understand the two modes of operation in a Ficht engine it is best to start with some fundamentals of engine operation. I promise to not make you into an engine expert with too much info. Please note that the graphics on this page are not intended to show actual engine construction. They are simple drawings to help you understand how an engine functions.
| Gas burning engines that use a reciprocating piston perform four basic functions over and over. In a four stroke engine one function occurs every stroke. First is intake - a valve opens a passage to the intake manifold while the piston moves downward. This draws air/fuel mixture into the cylinder. |
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Next is compression. The intake valve closes and the combustion chamber is sealed off. The piston moves upward and compresses the air/fuel mixture. This creates a mixture that burns better which helps create more energy. |
| Third is the power stroke. The spark plug ignites the fuel mixture. The burning fuel expands and creates pressure. This pushes on the piston and moves it downward. The act of the piston capturing the energy is how an engine converts chemical energy into mechanical movement. |
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The last step is exhaust. A second valve opens while the piston starts moving upward. This pushes the exhaust out of the engine and into the exhaust manifold. At the top of the stroke the exhaust closes, the intake opens and the whole thing starts again, intake, compression, power and exhaust. |
In a four stroke engine a fuel charge gets ignited every other time the piston moves upward. There are a lot of details involved in all this but the simple explanation here will do for our purposes.
A two stroke engine performs the same four functions but as it's name implies it does it all in two cycles. Instead of valves it uses openings on the sides of the cylinder called ports. On one side of the cylinder is the intake port and on the opposite side is the exhaust. When the piston rings are above the port openings the combustion chamber is sealed off (for compression and power). When the rings move below the ports they become open, somewhat akin to a valve opening in four stroke.
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In a carbureted two stroke when the intake port is open a slightly pressurized air/fuel mixture pushes into the cylinder. The piston moves upward, closes off the ports and compression starts. The fuel is ignited, the piston is pushed downward and eventually both ports are opened. The exhaust port opens slightly ahead of the intake and the exhaust gases start moving in that direction. When the intake port opens the pressurized fuel mixture rushes in and helps move the exhaust out of the engine. The piston hits the bottom of it's travel,starts to move upward and the whole thing happens again. This type of engine has the intake and exhaust occurring at the same time. The compression and power strokes occur in the upper part of the cylinder. A two cycle engine ignites fuel every time the piston travels up.
The action of the fresh fuel pushing the exhaust out is called scavenging. One problem with this two stroke design is that some of the fresh fuel mixture is lost out the exhaust port. This loss is actually designed into the engine to ensure all burnt fuel is removed (i.e. - an engine might be designed to produce 110% scavenging). For many years one of the challenges of engine design was minimizing this loss.
The Ficht technology has a cure for a lot of this problem. Most of the benefits occur in the lower RPM range when it is operating in the stratified mode (roughly under 1800 rpm). This name comes from the fact that in this mode the air/fuel ratios varies through out the cylinder, the various ratios exist in layers. During this mode while the exhaust is being purged from the cylinder no fuel is being injected. Instead of having an air/fuel mixture entering through the intake there is only air. No fresh fuel escapes out the exhaust port. When the piston has moved upward and the ports are closed the ignition and injector go into operation. First the spark plug starts to fire. Then just a third of a split second later fuel is injected into the engine directly on the spark plug. Since this is a multi spark engine all of the fuel is ignited. A very clean burning mode.
The other mode of operation is the homogeneous mode. This name is used because the air and fuel is evenly mixed and dispersed throughout the cylinder. The injector fires a fuel charge much earlier, the piston is close to the bottom of it's travel. As the piston moves upward it runs into the fuel plume and that further disperses it into the cylinder, completely mixing it with the air. The mixture compresses and the spark is fired 4 or 5 times (the dispersed fuel fires easier - requires less spark). Because the exhaust port is open while there is fuel in the cylinder some of it is lost out the port. The greatest loss occurs at wide open throttle. Still, it is cleaner than a carb engine at WOT.
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