The frequently asked Questions about the Z engine
Q: Aren’t there losses during gas exchange (intake
cycle) because of the high delivery pressure of intake air?
A: Some of the compression and transport work is converted
into kinetic energy (swirl, turbulence) and heat. The simulations
prove that these losses are gained back in other parts of the
process.
Q: Doesn’t the intercooling after the piston compressor
decrease the overall efficiency, when heat is removed from the
process?
A: Yes it does. The intercooling is needed to get the intake air
volume low enough at high loads. To optimize the efficiency, the
intercooling must be adjustable to decrease the level of
intercooling towards lower loads.
Q: What’s the difference between Z engine and common
2-stroke engine?
A: Z engine utilizes poppet valves and hasn’t any ports in
the cylinder wall for scavenging. There isn’t a 2-stroke
type scavenging in Z engine.
Q: How can Z engine be compared to 4-stroke engines?
A: Regarding the process:
The work cycle is similar compared to 4-stroke work cycle. The
exhaust, intake and compression cycles are shorter and part of
the compression is done externally.
Regarding the mechanical design:
The number of working cylinders of Z engine is half compared to
equivalent 4-stroke engine. Z engine has an integrated piston
compressor, intercoolers and first stage compressor (a turbo
charger or screw compressor).
Q: Is there more heat losses in the high swirl
combustion?
A: Yes there tends to be. However, excess heat loss can be
prevented by certain technical solutions.
Q: What’s the thermodynamic difference between swirl
chamber and the high swirl Z combustion?
A: In Z combustion, the hydrocarbon emissions are lower because
of the open combustion chamber. The heat losses are also
lower.
Q: What is the idea of homogeneous combustion?
A: The fuel is not sprayed directly into the flame and the
droplets are evaporated before local ignition.
Q: Why is the piston compressor driven trough the main
cylinder connecting rod lower end?
A: The main reason is in integration and in minimizing the size
of the compressor. Also, the track of the compressor cylinder
connecting rod lower end is elliptical due to this arrangement.
This results proportionally lower piston side forces.
Q: Why would a passenger car manufacturer choose Z
engine?
A: There are savings in the manufacturing costs.
Q: When will be the first Z engine in a car?
A: We are looking for a partner in automotive industry.
Q: Have you done any simulations of the Z engine?
A: The Z engine has been simulated with 0-d, 1-d and 3-d simulation software. For example, GT Power and Star CD have been used. At the moment (14.09.2005), a simulation project with Diesel-RK software is ongoing.
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