An Innovative Concept for aCompact Near-Zero-EmissionAuxiliary Power Unit

There is a growing demand for an independent source of heat and an increased supply of on-boardelectricity. Enginion’s new sub-compact Ezee technology seems to be a solution.

The technical innovations encom-passing the latest vehicle genera-tions have led to a dramatic risein the demand for on-board elec-trical energy. At the same time,the increasing efficiencies oftoday´s car engines suddenly cre-ate a serious dilemma, since theyno longer generate enough wasteheat for maintaining a comfort-able cabin temperature in coldconditions. There is a growingdemand for an independentsource of heat and an increasedsupply of on-board electric powerwhich can be made availableregardless of the engine’s operat-ing mode. An APU (AuxiliaryPower Unit) based on enginion’snew sub-compact Ezee technolo-gy seems to be the ideal solution

for meeting the energy require-ments of mobile applications. AnEzee APU offers both electricaland thermal energy while com-bining the lowest pollutant emis-sions with virtually no vibrations,as well as offering a high level offlexibility with regard to the fuelused (e.g. gasoline, diesel, naturalgas, etc.).

During the past five years, adrive technology has been devel-oped that could be an alternativefor a variety of drive applications.The technology is based on athermal reactor which, in additionto being capable of processingfossil and regenerative fuels withnear zero emissions, is silent, infi-nitely variable in its power outputand remarkably compact. This

Caloric Porous Structure Cell (CPScell) has been modified and opti-mized for application in driveunits. In order to convert the fuelenergy into mechanical power asefficiently as possible, a drivetechnology was developed aroundthe CPS cell which, in mostregards, is equivalent or superiorto conventional internal combus-tion engines. Some of its benefitsare unique:

• Extremely low emissionswithout any exhaust gasaftertreatment (NOx and COat the limit of measurability,no HC emissions)

• Very high torque, power out-put equivalent to dieselengines

by Herbert Clemens, Michael Hoetger, Oliver Mehler, enginion AG

Figure 1: APU based on enginion’sEzee technology, 6 kWelectric /25 kWthermal

Figure 2: Caloric Porous StructureCell, lab version with 36 kWthermal

Dramatic rise foron-board electri-cal ernergy.

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45AutoTechnology 2/2002

46 AutoTechnology 2/2002

• Fuel flexibility (gasoline,diesel, natural gas, biofuels,hydrogen, etc.)

• Thermal and kinetic energy-output (both independentlyvariable)

• High efficiency at all loads• Vibration-free and quiet• Compact and robust• Oil-free lubrication• Low production costs

CPS CellThe Caloric Porous Structure Cell(CPS cell) is a thermal reactor inwhich the combustion process ofa given fuel takes place within aporous matrix. This technologyallows flame stabilization at avery homogeneous temperaturedistribution in the range from1200 °C to 1300 °C. Unlike ordi-nary combustors with an openflame, this results in a great vari-ety of advantages. The mostnotable features in this contextare not only its extremely low-emission operation (< 4 ppmNOx) but also its broad powermodulation (infinitely variablefrom 1.5 to 36 kW, thermal), aswell as its extremely compactsize, freedom of shape and multi-fuel capabilities. The CPS cellconsists of a porous ceramicmaterial. The distribution of thepore size within the CPS cell canbe designed in such a way that alarge variety of fuels, such as nat-ural gas, hydrogen, propane,butane and all common automo-tive fuels, can be processed. Onlya special vaporization unit is has

flue gas flows past an expansionunit and heats a stack of super-heating tubes, before reaching asteam generator. The residual heatof the flue gas is finally trans-ferred to the incoming feed waterusing a heat exchanger. The rela-tively cold gas exits through anexhaust pipe. Neither a silencernor exhaust-gas aftertreatmentare required. The working mediumis kept in a closed cycle. Beforeentering the engine, it is pressur-ized with the aid of a feed waterpump. The rated pressure for thesmall and cost-effective units is50 bar, while the higher-perform-ance class works at 300 to 500bar. This case is equivalent to asupercritical cycle with a waterdensity of 25 % of liquid water atpeak temperature and pressure. Inthe exhaust steam and exhaustgas heat exchangers, the feedwater absorbs the residual heatand then flows into the steamgenerator. Here, it completelyevaporates and reaches a temper-ature of up to 500 °C. This steamis injected and further superheat-ed in the superheater unit.Depending on the load and rota-tional speed, it can reach temper-atures of up to 900 °C. In theSteamCell, this highly energeticsteam releases its energy to thedrive, while it is further heated bythe high-temperature flue gaseswhich are passing the outside ofthe expansion unit. At the end of

Absence of com-plex internalcombustion

mechanisms.

Figure 3: Measurement data of the lab version CPS cell

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been developed, allowing the sys-tem to use liquid fuels.

Ezee TechnologyThe engineering and design focusduring the Ezee Technology‘sfrom-scratch development wasthe consideration of the costaspects of all assembly groupsand components. The thermalengine presented here constitutesa radically new approach. This”SteamCell” runs entirely withoutoil lubrication. Depending on itssize and type, the engine useseither water-based lubricants orno lubricant at all. The basicengine does not need to be cooled.This and a thorough design of theheat exchanging units guaranteelow heat losses and thereforegood efficiency.

The absence of complex inter-nal combustion mechanismsallows for the straightforwarddesign of customized enginesaccording to varying require-ments. A fixed rotational speedfrom 0 to 3000 rpm or variableengine operation to provide large-ly independent outputs of electricand thermal energy are possibleoptions.

Operating PrinciplesBy means of a controllable fan,the combustion air is aspiratedthrough a filter and guided alongthe peripheral walls to the rearparts of the engine. At the sametime, heat is transferred from theinner parts of the engine to theinducted air, resulting in a surfacetemperature of only max. 40 °C. The pre-heating ofthe air creates favour-able conditions forthe subsequent fuele v a p o r a t i o n ,which takes placein the rear partsof the engine. Thec o m b u s t i b l eair/fuel mixture isadjusted to an opti-mum mixture ratioand then supplied to the CPScell. A glow plug inside the cellensures that the initiation of thecombustion process occurs whenthe engine is started.

After its complete oxidationwithin the cell, the resulting hot

Figure 4:APU based onenginion’s Ezeetechnology, varioussizes from 1 to 400 kWelectric

47AutoTechnology 2/2002

neural networks and adaptivediagnostic systems. In addition tothe basic process control tasks ofthe APU and the battery chargingcontrol unit, the APU’s control unitcan also take over the total energymanagement within the vehicle.This releases other vehicle controlunits from similar tasks. Intelligentback-up functions can also bemanaged by the APU, e. g. switch-ing to back-up lamps when a cor-responding rear blinker light fails.

In order to give a generalimpression of the Ezee’s capabili-ties, a comparison of the fuel con-sumption and exhaust emissionsis shown for a 50 kWmechanicalEzee vehicle propulsion system.Because of its high torque, thisengine, when installed in a mid-size car, would have a drivingperformance comparable to corre-sponding diesel and spark-igni-tion engines in this vehicle class.The following figure shows theresulting fuel consumption andexhaust gas emissions comparisonin the U.S. FTP-75 test cycle. Itcan be seen that the Ezee operateswell below the limits of theworld’s most stringent emissionlegislation for mass producedvehicles (SULEV in the USA) with-out any exhaust gas aftertreat-ment. At the same time, itachieves a fuel consumption closeto that of modern diesel engines.

the expansion process, the steamleaves the SteamCell throughexhaust ports. This exhaust steamis used to transfer residual heat tothe fresh feed water, after which itreaches a condenser, where it istransformed back into the liquidstate. A small water tank and afeed water pump close the cycle.The kinetic energy produced by theSteamCell drives a DC generator.

The energy of condensation isabsorbed by the vehicle’s coolantfluid. The thermal engine can becontrolled in such a way that itprovides auxiliary heat to thecoolant as required. Therefore, itis able to heat up the passengercompartment to any convenienttemperature at any given time,even when the engine is off. It isadditionally possible to use thisfunction during engine cold startto reduce engine wear and emis-sions.

The APU is equipped with acontrol unit which is suitable forin-vehicle application. The con-trol unit uses a connection to thevehicle-specific bus system (e. g.CAN). At the moment, it employsa Siemens 80C167 processor as acore, but this is expected to bereplaced in the near future by aMotorola MPC555. The controlunit combines a whole range ofnewly developed functions andapproaches, including artificial

[1] G. Buschmann, H. Clemens, M.Hoetger, Dr. B. Mayr; Zero EmissionEngine – Der Dampfmotor mit iso-thermer Expansion,Motortechnische Zeitschrift 61(2000), Heft 5

[2] J. Beilharz; Hardware-in-the-LoopSimulation des dynamischenVerhaltens einesGegenstromwärmetauschers, VDIBerichte 1534, VDI Verlag, 2000

[3] B. Mayr, G. Buschmann, M.Hoetger, H. Clemens; Zero EmissionEngine (ZEE) – Der isothermeDampfmotor als Fahrzeugantrieb,VDI Berichte 1565, VDI Verlag,2000

[4] B. Mayr, G. Buschmann, M.Hoetger, H. Clemens; DerDampfmotor, Entwicklungsstandund Marktchancen,Motortechnische Zeitschrift 62(2001), Heft 5

Figure 6: Fuelconsumption

Figure 5: NOx emissions

Neither a silencernor exhaust-gasaftertreatmentare required.

Specifications

Example: max. 6 kWelectric, max. 25 kWthermal

Generator depending on customer requirements

Fuel:Gasoline, diesel, alcohol, hydrogen, natural gas, etc.

Noise:max. 54 dB (generator mode + heat mode)max. 45 dB (heat mode)

Dimensions:L 450 mm, H 360 mm, W 160 mm

Weight: 32 kg

Vibrations:less than 1 N dynamic load per mount and direction

Surface Temperature: less than 40 °C

Start-up times: Heat after approx. 2 sec. (cold start), Electricity afterapprox. 20 sec. (cold start), <2 sec (warm start)

Max. Fuel Effidiency: 94% ( only heating), 92% (heat and power), 25% ( only power).

Emissions:NOx 4 ppm, CO 2 ppm, HC 0 ppm

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