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4-stroke cycles compressed to single crankshaft revolution (Atkinson cycle)
Fully valve controlled gas exchange
Diesel or Otto engine
Turbo charger and supercharger (piston compressor)
2-cylinder Z engine provides equal power output to a 4-cylinder 4-stroke
engine
HCCI combustion
Internal EGR
Easily balanced mass forces
Good torque characteristics
Ignition controlled by multiple variables
High downsizing degree
Excellent transient behaviour
Driving fun
What is Z engine?
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4/2-stroke, 2-cylinder engine
Revolutionary working principle combines the best aspects of 2- and 4stroke engines
Part of the compression cycle is made outside of the working cylinder, so all
of the cycles of 4-stroke engine can be done in a single crankshaft
revolution
Compact size
Light weight
Small emissions
Low manufacturing costs
Exhaust cycle
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Exhaust valves opens 60°
BBCD and closes 120°
ABCD
 2 x 180° = 360° pulses
for the turbo charger
Exhaust gases hot enough
for 3-way catalyst
Injection
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Fuel injected during 110° 120° ABDC, when the
exhaust valves are closing
Long mixing time before
the ignition, 60° – 70°
Injection pressure 200 –
700 bar, duration 5° – 12°
Hollow cone spray
Small spray penetration
Small droplets
Fuel injected to hot
exhaust gas
 Partial fuel reforming
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High temperature and low
pressure during injection
 Rapid fuel evaporation
Gas temperature an
pressure during the start of
the injection: 700 – 800 K,
1,5 – 2,5 bar
Temperature drop of the gas
in the cylinder during
injection: 200 – 400 K
Heat for fuel evaporation
from exhaust gas
The temperature and pressure
curves between 80° - 40° BTDC
Intake cycle (scavenging)
• Intake valves opens 60°
BTDC and closes 45°
BTDC
• Intake pressure 4 – 15
bar
 Velocity of intake gas:
300 – 500 m/s
• Intern EGR 15 – 45%,
acts as an
intern heat
exchanger
• Hot, active radicals in
EGR can be used to
assist ignition
• No overlapping of intake
and exhaust valves
 No losses of intake
gas
• Fuel evaporation cools
the mixture: more air to
the cylinder
• Electric heater in the
intake channel for start
The theorethical valve flow
Final Compression
• Mechanical compression
ratio: 14 – 15:1
• Primary compression is
made in piston
compressor, secondary
in work cylinder: 3-5:1
• Short compression time
 Low amount of heat
transfer
• Fuel evaporation before
final compression and
high intercooling rate
 Low compression
temperature, more air in
to the cylinder
• Compression
temperatures at TDC:
800 K at part load, 700 K
at full load
 The compression
temperature descend
when load increases
• Lower gas temperature
 Lower compression
pressure, higher bmep
Ignition delay curve of HCCI mixture
PV diagram of the Z engine
Combustion and work cycle
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SAHCCI (Spark Assisted
Homogenous Charge
Combustio Ignition)
Controlled By: Temperature
at TDC, lambda, injection
amount and timing,
intercooling rate, valve
timing
Pressure and temperature at
TDC controlled by adjusting
intake air pressure and
temperature
Low temperature at TDC: no
self ignition
Start of combustion: 5-15°
ATDC
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Short combustion duration:
high efficiency
Lambda 1.7-1.9: low Tmax,
low NOx
Active radicals assist the
ignition
Active radicals lower CO
and HC
No knock, as ignition at the
right side of NTC area
Manufacturing costs compared to 4-cylinder turbodiesel
engine equipped with Common Rail + DeNOx-catalyst +
particulate filter = 2800 €
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200 €
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0€
-200 €
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-400 €
-600 €
-800 €
-1 000 €
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-1 200 €
-1 400 €
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2 working cylinders less
= - 600 €
Compressor needed
= + 200 €
Low injection pressure,
2 low cost nozzles
= - 400 €
No DeNOx catalyst
= - 500 €
No particulate filter
= - 100 €
Together = - 1400 € lower
production costs per
engine!