Irish Research Council Enterprise Scheme & Ingersoll Rand International


Barry Flannery

Starting date


Finishing date


Summary and objectives

Heavy trucks accounted for 3.2% of global energy consumption in 2010. Trucks idle their main engine on average for 1860 hours per year as it is necessary to provide power for “hotel loads” during mandated driver rest periods in the United States. The hotel load is comprised of a cab air conditioning load, space heating load and electrical power load for appliances including cookers, microwaves and TVs.

Idling is highly fuel inefficient, polluting, and adds unnecessary wear to the main engine and so the practice has been heavily restricted in many US states Auxiliary power units (APUs), consisting predominantly of more suitably sized diesel engines and vapour-compression (DEVC) refrigeration systems, are instead used to provide for this hotel load. However, these APUs face difficulties of their own.

Combustion in diesel engines is noisy and produces many unwanted emissions such as oxides of nitrogen (NOx), carbon monoxide (CO) and diesel particulates or soot. Expensive after-treatment is necessary to comply with regulations imposed by bodies such as the California Air Resource Board (ARB) and the cost of these aftermarket components often exceeds the cost of the diesel engine itself. Environmentally damaging hydrofluorocarbons (HFCs) such as R-134a are used in the DEVC APU vapour-compression cooling system as refrigerants. The impending Montreal Protocol phase-down of HFCs combined with increasingly more stringent emissions legislation make the long-term viability of diesel engine-vapour compression (DEVC) technologies uncertain.

The goal of this research project is to investigate the technical feasibility of a hybrid free-piston Stirling engine and zeolite-water adsorption chiller system used as an auxiliary power unit for heavy truck applications.

The proposed system could potentially offer the following benefits:

  • Can run on any liquid fuel (or even gaseous fuel if modified appropriately)
  • Virtually silent
  • Clean emissions without after treatment (diesel particulate filtering)
  • Ultra reliable
  • No refrigerants required
  • Cooling system able to run off main truck engine waste heat (if integrated appropriately)

The system also poses a number of technical questions:

  • Can an adsorption cooling system reach the specific cooling power required for this application?
  • Can the coupled system fit within the existing envelope and meet mass requirements with current technology?
  • Can the system operate in the expected environmental conditions (ambient temperature, vibration profiles...etc.)?
  • What fuel savings (if any) does this configuration offer over existing diesel engine technology?

Projected research outputs

Establishment of an APU research laboratory with the following test rigs:

  • 1 kWe gas-fuelled free-piston Stirling engine
  • 1 kWe diesel-fuelled kinematic Stirling engine
  • TriPac Evolution diesel-fuelled truck APU

Development of an integrated system level model of the proposed hybrid Stirling-adsorption system using a physical-based modelling language such as Modelica or MathWorks SimScape.

Academic outputs

  • Several research poster presentations
  • Multiple journal and conference paper publications

Conferences proceedings

B Flannery, R Lattin, O Finckh, H Berresheim, RFD Monaghan. 
Development and experimental testing of a hybrid stirling engine-adsorption chiller auxiliary power unit for heavy trucks. 17th International Stirling Engine Conference and Exhibition, Newcastle, United Kingdom, Aug 2016

B Flannery, O Finckh, H Berresheim, RFD Monaghan. Hybrid stirling engine-adsorption chiller for truck auxiliary power unit applications. 12th IIR Gustav Lorentzen Natural Working Fluids Conference, Edinburgh, United Kingdom, Aug 2016

Flannery B, Lattin R, Berresheim H, Monaghan RFD. Hybrid Stirling Engine‐Adsorption Chiller for Truck APU Applications. International Stirling Engine Conference,Bilbao, Spain, Oct 2014

Journal publications

Hybrid Stirling engine-adsorption chiller for truck auxiliary power unit applications. B Flannery, R Lattin, O Finckh, H Berresheim, RFD Monaghan. 2017.  International Journal of Refrigeration 76, 464-471

Development and experimental testing of a hybrid Stirling engine-adsorption chiller auxiliary power unit for heavy trucks. B Flannery, R Lattin, O Finckh, H Berresheim, RFD Monaghan. 2017. Applied Thermal Engineering 112, 464-471


Truck Idling - USEPA

Stirling Engine Background - Electric Power Research Institute US