2 4-stroke cycles compressed to single crankshaft revolution (Atkinson cycle) Fully valve controlled gas exchangeDiesel or Otto engineTurbo charger and supercharger (piston compressor)2-cylinder Z engine provides equal power output to a 4-cylinder 4-stroke engineHCCI combustionInternal EGREasily balanced mass forcesGood torque characteristicsIgnition controlled by multiple variablesHigh downsizing degreeExcellent transient behaviourDriving fun
3 What is Z engine? 4/2-stroke, 2-cylinder engine Revolutionary working principle combines the best aspects of 2- and 4-stroke enginesPart 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 revolutionCompact sizeLight weightSmall emissionsLow manufacturing costs
4 Exhaust cycle Exhaust valves opens 60° BBCD and closes 120° ABCD 2 x 180° = 360° pulses for the turbo chargerExhaust gases hot enough for 3-way catalyst
5 InjectionFuel injected during 110° - 120° ABDC, when the exhaust valves are closingLong mixing time before the ignition, 60° – 70°Injection pressure 200 – 700 bar, duration 5° – 12°Hollow cone spraySmall spray penetrationSmall dropletsFuel injected to hot exhaust gas Partial fuel reformingHigh temperature and low pressure during injection Rapid fuel evaporationGas temperature an pressure during the start of the injection: 700 – 800 K, 1,5 – 2,5 barTemperature drop of the gas in the cylinder during injection: 200 – 400 KHeat 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° BTDCIntake pressure 4 – 15 bar Velocity of intake gas: 300 – 500 m/sIntern EGR 15 – 45%, acts as an intern heat exchangerHot, active radicals in EGR can be used to assist ignitionNo overlapping of intake and exhaust valves No losses of intake gasFuel evaporation cools the mixture: more air to the cylinderElectric heater in the intake channel for start
9 Final Compression Mechanical compression ratio: 14 – 15:1 Primary compression is made in piston compressor, secondary in work cylinder: 3-5:1Short compression time Low amount of heat transferFuel evaporation before final compression and high intercooling rate Low compression temperature, more air in to the cylinderCompression temperatures at TDC: 800 K at part load, 700 K at full load The compression temperature descend when load increasesLower gas temperature Lower compression pressure, higher bmep
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 timingPressure and temperature at TDC controlled by adjusting intake air pressure and temperatureLow temperature at TDC: no self ignitionStart of combustion: 5-15° ATDCShort combustion duration: high efficiencyLambda : low Tmax, low NOxActive radicals assist the ignitionActive radicals lower CO and HCNo 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!
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