Post on 01-Apr-2015
transcript
• 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 €
• Compressor needed = + 200 €
• 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!