2. 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

3. What is Z engine? 4/2-stroke, 2-cylinder engine
Revolutionary working principle combines the best aspects of 2- and 4-stroke 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

4. Exhaust cycle 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

5. Injection
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
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

6. The temperature and pressure curves between 80° - 40° BTDC

7. 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

8. The theorethical valve flow

9. 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

10. Ignition delay curve of HCCI mixture

11. PV diagram of the Z engine

12. Combustion and work cycle
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
Short combustion duration: high efficiency
Lambda : 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

13. Together = - 1400 € lower production costs per engine!
Manufacturing costs compared to 4-cylinder turbodiesel engine equipped with Common Rail + DeNOx-catalyst + particulate filter = 2800 €
2 working cylinders less = €
Compressor needed = €
Low injection pressure, 2 low cost nozzles = €
No DeNOx catalyst = €
No particulate filter = €
Together = € lower production costs per engine!