The Z engine

What is the Z engine?

• 4/2-stroke, 2-cylinder engine• Revolutionary work 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 rotation• Compact size• Light weight• Small emissions• Low manufacturing costs, no after treatment needed

• 4-stroke cycles compressed to single crankshaft rotation (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 with ignition injection = single fuel RCCI• Internal EGR• Easily balanced mass forces and mass moments• Good torque characteristics• High downsizing degree• Excellent transient behaviour• Good driveability

The work cycle of the Z engine

Z-engine allows providing the same power in two working cylinders as conventional 4 stroke diesel engine in 4 cylinders, downsizing and low manufacturing cost are achieved.

Exhaust cycle

• Exhaust valves open 50° BBCD and close 120° ABCD 2 x 180° = 360° pulses for the turbo charger

• Exhaust gases hot enough for oxicat

Injection

• Fuel injected during 110° - 120° ABDC, when the exhaust valves are closing

• Long mixing time before the ignition, 60° – 70°

• Injection pressure 700 – 1200 bar, duration 5° – 12°

• Hollow cone spray• Small spray penetration• Small droplets• Fuel injected to the hot internal

exhaust gas Partial fuel reforming

• High temperature and low pressure during the injection Rapid fuel evaporation

• Gas temperature and pressure during the start of the injection: 700 – 800 K, 1,5 – 2,5 bar

• Temperature drop of the gas in the cylinder during the injection: 200 – 400 K

• Heat for the fuel evaporation from the internal exhaust gas

Intake cycle (scavenging)

• Intake valves opens 60° BTDC and closes 45° BTDC

• Intake pressure 4 – 20 bar Velocity of the intake gas: 300 – 500 m/s

• Internal EGR 15 – 45%, acts as an intern heat exchanger

• Hot, active radicals in the EGR can be used to assist the ignition

• No overlapping of the intake and exhaust valves No losses of the intake gas

• Fuel evaporation cools the mixture: more air to the cylinder

• Electric heater in the intake channel for the cold start

• Glow plug for the cold start

The temperature and pressure curves between80° - 40° BTDC = during the fuel injection and intake

Final Compression

• Expansion ratio: 15:1 – 17:1• Primary compression is

made in piston compressor, secondary in the 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 decreases when the load increases

• Lower gas temperature Lower compression pressure, higher bmep

Ignition delay curve of the HCCI mixtureAnd the ”safe operation area” marked

Combustion and work cycle

• Single fuel RCCI, ignition injection close to TDC

• Controlled By: Temperature at TDC, lambda, ignition injection amount and timings 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: 0 -15° ATDC

• Short combustion duration: high efficiency

• Lambda 1.7-1.9: low Tmax, low Nox, no aftertreatment needed

• Active radicals assist the ignition

• Active radicals lower CO and HC as well as the high enough combustion temperature, 1700 – 2000 K

• No knock, as ignition allways at the right side of NTC area

Diesel – RK & In-cyliner parameters

Manufacturing costs of the Z-engine compared to a 4-cylinder turbodiesel engine equipped with

Common Rail + DeNOx-catalyst + oxicat + particulate filter = 2800 €

• 2 working cylinders less = - 600 €• Compressor needed = +200 €• Low injection pressure, low cost nozzles = - 400 € • No DeNOx catalyst = - 500 €• No particulate filter = - 100 €

Together = - 1400 € lower production costs per engine!