• 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?

• 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

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

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

The temperature and pressurecurves 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

• 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 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 ۥ 2 working cylinders less

= - 600 ۥ Compressor needed

= + 200 ۥ Low injection pressure,

2 low cost nozzles = - 400 €

• No DeNOx catalyst = - 500 €

• No particulate filter = - 100 €

-1 400 €

-1 200 €

-1 000 €

-800 €

-600 €

-400 €

-200 €0 €

200 €

2 working cylinders less

Compressor needed

2 low cost nozzles

No DeNOx catalyst

No particulate filter

Overall

Together = - 1400 € lower production costs per

engine!