Stirling Engine Report 1 - Hardware Testing

Stirling Engine Progress Report 1

The Stirling engine was shipped over from Thermo King's R&D Division in Minneapolis, USA and arrived in Thermo King Galway in early December. I then transported the engine from Thermo King to my home in Oranmore in order to clean it up and verify that it is fully operational in advance of the project. Much of the work undertaken in this report was done sporadically over the Christmas holidays.

Whispergen PPS16 Marine Stirling Engine in the boot of my car after collection from Thermo King. The unit weighs about 100kg which makes lifting and transporting it a challenge.

 

Condition of the engine as received from Thermo King. Much of the plumbing was modified as per requirements of Thermo King Minneapolis R&D Division most of the wiring was in a mess and disconnected.

Simply reconnecting the plumbing and electrics to the factory settings was a difficult and confusing job. The engine appears to have been stored without its cover and has literally been gathering dust over the years. There appears to be little or no corrosion of key parts.

The Stirling Engine is a pressurized system filled with nitrogen at 24 Bar. One of the worries of the prolonged storage was progressive leaking of the nitrogen working fluid and the possibility that the engine may need to be recharged with nitrogen. Obtaining pressurized pure nitrogen is a relatively straightforward task however gas regulators capable of discharging in excess of 10 Bar are very specialized and uncommon. The charging valve on the unit is a  1/4" NPT schrader valve.  The appropriate gas lines and valve fittings were borrowed from Thermo King along with a pressure gauge to check pressurization. Luckily the system appears to have maintained pressure and is not in need of a nitrogen refill.

Pressure gauge with hose lines.

James Nallen generously supplied me with two DAQ units. These will be used for monitoring any additional thermocouples that are required to monitor the system. Additionally, a pressure transducer to monitor engine nitrogen pressurization and fuel flow transducer may be incorporated in the measurement system. Luckily the Stirling engine has an advanced onboard microprocessor that is equiped with many sensors.

The Stirling engine's microprocessor is powered from the same 24 V battery bank that it discharges generated power into. Therefore, in order to test that the engine is functional it was necessary to obtain a pair of 12 V batteries. Thermo King kindly supplied me with some second-hand gel cell batteries. 

Pair of gel cells being charged using two charge controllers.

In order to test the unit it was necessary to build a small workbench in my workshop to accomodate easy access to the engine. Both front and back access would be required to reconnect the various electronics and sort out the plumbing. It was necessary to lift the engine out of its enclosure to clean it down and access hard-to-reach areas. 

Work area consists of a set of thick wooden laths with a sheet of plywood spanned between two benches. 

Engine in-situ. Note chief technician in the background (my Dad).

Engine being lifted out of its enclosure for cleaning.

Alternate view


Rear view of engine

View of the untangled electronics. The additional shunts and various external voltage measurement hardware was removed. This was being used by technicians in Thermo King Minneapolis. It is my intention to use the onboard sensors to perform this (Thermo King did not have access to the controller software at the time). For the purposes of unit testing, it is unnecessary. Many of the unit sensors are still disconnected and unidentified. It will be necessary to identify these using the unit schematics.

View of the unit connected to the battery bank. The microcontroller was powered up for the first time and the electronics appear functional.

 

Engine sensors fully connected, identified and labelled. Note Dad cleaning the fuel pump.

 

Make-shift primary cooling loop test. Note advanced header tank technology (white funnel!) The system is now just charged with water and bled of air. I have only charged it with water as a temporary measure to test pumps and subsystems. The actual working loop will be water with glycol and a corrosion inhibitor with a proper header tank. 

Overview of current temporary plumbed circuit to test the system. All that is left to be done is make a fuel delivery system and bleed it of air. A temporary exhaust system is also required.

Some high temperature exhaust ducting and some additional water hose, both courtesy of Thermo King.

  

The Engine is now operational and can be powered up for short periods of time (the tiny heat reservoir limits run time to about 10 minutes before the coolant begins to boil).