FICHT and E-Tec Notes
FICHT and E-Tec Notes
How does a 2 stroke FICHT engine work?
A two stroke engine performs the same four functions as a four cycle engine 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.
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.
How does the FICHT MAP work?
The FICHT MAP system comes from the term ‘fuel map’. A very basic definition of MAP is ‘A set of instructions used by a fuel injection Electronic Control Unit.’ The ECU reads a number of inputs (sensors) and uses that info to give a specific output (spark timing and fuel output). This is done many many times a second in an attempt to keep engine systems adjusted for various conditions.
If a system was designed with just two inputs you could make a graphical representation of the MAP that might look like a spreadsheet. For any two input values there would be one set of data to use as an output.
If you design a system with three inputs the graphical representation would look like a very complex 3D graph, lots of peaks and valleys.
A Ficht ECU uses six inputs (throttle position, crankshaft position sensor, water temperature, air temperature, alternator voltage and barometric pressure) as well as a calculated torque output to determine spark timing, spark duration, injector timing, injector duration, injector current, and oiling output. Needless to say a MAP for such a system is quite an undertaking to create.
I don’t have a lot of knowledge on how a MAP is created but I’m sure that a lot of it is worked out on a computer. I do know that a bit of it is done through hard work and trial and error. An engine is run, monitored, conditions are varied, results are recorded and studied and the final MAP is hammered out. When it all looks good it is released for the public to use. That is when the education starts.
People use engines many different ways, each person with their own touch and each with their own boat setup. Not every possibility gets duplicated in a research setting (and I doubt if that could ever happen). With the Ficht MAP the biggest problem developed with flats boats. The load on the engine didn’t match what the MAP expected and that resulted in a poor midrange performance.
The Ficht ECU records data and with the right program the information can be downloaded into a computer. The data is analyze and a new map program is developed. The change might be as simple as firing an injector slightly later during a certain rpm range. This new program can be uploaded into the ECU with a laptop.