The engines

The crowd funding project engine

So far, we have built and tested a small, 15 Watt engine with a piston diameter of 50 mm (2″), and a stroke of 150 mm (6″). Now, we want to go bigger and build, test and run a 2 kW engine with a piston diameter of 220 mm, and a stroke of 450 mm. The design expansion ratio is n = 1:3.

Our first engine will be based on the Mk 2 model. Since crowd funding will very probably not allow to experiment with e.g. new components or lay-outs, we decided to minimise risk by building a 1:5 scaled up version with a classic lay-out first. This engine configuration with a beam to link piston rod and drive shaft is quite large (which does not really affect us at this stage) but has the advantage that all components are freely accessible, so that repairs or modifications are very easy. The next figure shows the engine:

side-and-front
The 2 kW Engine

With an overall length of 1.8 m (6 ft ), a width of appr. 0.9m (3 ft) and a height of 1.6 m (5 ft 4″) it is quite a large engine. The design incorporates several improvements:

  1. The flywheel now has a 1:3 gearing, improving its effect on power output quality.
  2. Power take-off is a DC permanent magnet  generator.
  3. The piston rod seal detail is much improved
  4. The condenser will probably be a heat exchanger which allows to (a) reduce final condensation temperature to 40°C with a condensation pressure of 0.07 bar   (absolute), and (b) produces exit cooling water temperature near the boiling point so that a smaller part (1/7 to be accurate) the water can be used to replenish the boiler, and the rest e.g. for heating.
  5. The load-bearing structure has moved away from an outside frame, and will be built mostly in plastic to reduce costs.

We are also looking at air-flow cooling (or, technically speaking, heat rejection) where we want to try out Venturi cooling which may allow to create temperatures below ambient without a refrigerator… watch this space …

Further improvements, the follow-up configuration

the beam engine is quite large, and contains several elements which could be replaced with simpler arrangements. In the design to be built withing the crowd funding project, we did not want to do his to avoid the situation where we have several experiments within an experiment, which of course increases risk quite dramatically.

The engine would also implement several improvements:

  1. The cylinder is horizontal, to reduce space demand.
  2. The condenser is evacuated and the condensate removed by an electric vacuum pump. This reduces the mechanical complexity, and the need to pump in every stroke.
  3. A modern flywheel is attached to the crank shaft

The following drawing shows how we imagine this engine at the moment:

engine-hor-black
The next stage, 2 kW, 250 mm diameter, 400 mm stroke engine

With this engine, we can generate electricity, and we can determine the performance at near full scale (which may be different than at model scale). We also get a better idea of practical design aspects as well as costs.