7/16/2019 Stirling DK Engines

http://slidepdf.com/reader/full/stirling-dk-engines 1/2

Sustainable power production

Stirling engines for biomassapplications

Engine models SD4E and SD8E

The external combustion of theStirling engine makes itvery attractive for small-scale Combined Heat

and Power (CHP) plants using bio-fuels. StirlingDanmark has developed a series of engines spe-cifically designed for power production from bio-mass.

The Stirling principle

Stirling engines are based on a closed cycle, wherethe working gas is alternately compressed in a coldcylinder volume and expanded in a hot cylindervolume. The heat input from the combustion of fuel is transferred to the working gas through ahot heat exchanger (the heater) at a high tem-perature typically between 950°C and 1050°C. Theheat drives the pistons, which drive the shaft for

power production. The remaining heat is trans-ferred to the water circulation system.

Description

The engine is designed as a hermetically sealedunit with the alternator incorporated in a pressur-ised crankcase. Only static seals are necessarybetween the Helium working gas in the crank caseand the surrounding air. All bearings are greasedand the engine is oil-free. Piston rings and pistonrod have been made from PFTE-based materialsfor “dry-running”. The internal design of the en-gine eliminates the need for high pressure pistonrod seals, which is known to give problems in mostother Stirling engine designs.

The four cylinder Stirling engine, SD4E, has anominal electric power output of 35 kW. The cylin-ders are arranged in a square, and Helium is used

as the working gas at amean pressure of ap-

proximately 4,5 MPa. The fourheater panels form a square combustion

chamber. The 8-cylinder SD8E engine rated at 75kW is basically two 4-cylinder engines connectedon the same shaft to a common alternator.The asynchronous alternator, which is also used asa starter motor, has 6 poles corresponding to anengine speed of approximately 1000 rpm whencoupled directly to the power grid.

The heater is designed specifically for direct com-bustion of biomass:

• Wide flue gas passages in the heater section

• Careful design of flow paths through the heater

• Large surface area per unit heat transferred

• Easy cleaning access of heater panels either

manually or by shock blasts.

 Application

The engine can run on almost any heat sourcewhich can deliver flue gases at approx. 1000°Cwith low or no particles and ashes. Depending onthe system design this could be from solid, liquidor gaseous fuels. Examples:

• Direct combustion of wood chips

• Gasification (indirect combustion) of wood chips

and other solid biomass

• Pyrolysis of difficult solid biomass fuels

• Combustion of biogas or bio-oil.

•

Combustion of waste products such as glycerine•  Add-on to large boilers on natural gas or bio-

mass 

Heater designed forbiofuels

Low maintenance pressurisedcrank case with oil-free bea-

rings

 Alternator integratedin hermetical design

Water circulation forengine cooling

Optimized Stirling cycledesign with high efficiency

regenerator

7/16/2019 Stirling DK Engines

http://slidepdf.com/reader/full/stirling-dk-engines 2/2

Stirling Danmark Tel: +45 45 25 93 70Diplomvej Fax: +45 45 25 93 71DTU, Building 373 South www.stirling.dk DK-2800 LyngbyDenmark 

Reliability

The engine has been designed for low mainte-nance and long life-time. The design life of theengine is 100.000 hours with 4000/8000 hoursservice intervals.

Research & Development

The current design is based on 15 years of re-search and development at the Technical Univer-sity of Denmark. 9 engines have been built withmore than 30.000 hours of operation. Researchand development is ongoing to e.g. increase effi-ciency and to implement new features.

Engine features

• Sturdy design and hermetically sealed for

long lifetime in dusty environments

• Oil-free mechanism with greased bearings.

No risk of oil contamination of heat trans-fer surfaces

• Few movable parts

• Patented yoke mechanism

• Non-hazardous helium working gas

• High electrical efficiency

• Heater designed for biomass combustion

• Proven design

• Thousands of man-hours of research and

development

• Competitive life-cycle cost

Specifications 

Engine type SD4E SD8E

No. of cylinders 4 8Bore 142 mm 142 mm

Stroke 76 mm 76 mmWorking gas Helium HeliumMean pressure 4.5 MPa 4.5 MPaEngine speed 1010 rpm 1010 rpmHeat output in water 90 kW 180 kWElectric power output 35 kW 75 kWNominal elec. efficiencyon gasification gas 28% 29%

Nominal cooling watertemperature 55°C 55°C

75 kW 8-cylinder engine

Heater for direct combustion applications