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Projects: The HOSSACK Engine


The Story:
As a young man I was inspired by the Wankel engine. Back then it was a very hot engineering topic and a regular feature in Popular Mechanics.  Many of the top auto manufacturers got involved. The clever internal geometry seduced many pundits, though its origins go back 50 years to the steam age.

Two-stroke engines don't usually idle as well as this.

That is because this one has asymmetric port timing.
Watch to the end of this video!

The Wankel engine had two well-known issues, sealing and poor combustion. Solve these problems and you had a compact low vibration world beater to rival the standard format. The first problem was primarily due to very high tip seal speed and a combustion problem was due to a poor flame front because of its squat combustion chamber.

Norman set out to find a midway between the Wankel and the conventional piston engine. The HOSSACK engine drew for each format. Norman set up a sort of mental matrix of the good and the bad characteristics of each type. So crank shaft was good and square, piston was good and Wankel combustion chamber was bad as was piston to cylinder wall loading. But maybe the wall loading could be made use of as a seal. Norman also didn’t like the piston accelerations at the top and bottom of the stroke of the conventional engine.

From these mental gymnastics the HOSSACK engine emerged. In about 1973 a very crude prototype was built and run. It was very simple but as it worked, it demanded a follow up.
The second prototype was a very different matter. This engine involved a full and detailed design exercise. This time patterns were made, then castings were made for the housings and a crank was acquired from a real 50cc 2 stroke engine. The engine had a stroke of 40mm with a lobe cross section of 50mm by 40mm making it an 80cc engine. The flywheel and ignition came from the donor engine and a Tilitson carburetor was sourced.

The engine was a runner in 1975 but it was not impressive. It ran but never for longer than 30 seconds at a time. At the same time Norman wrote to many of the major manufacturers trying to raise interest in the design. The feed back was negative and in some cases quite hostile and with the 30 second run unexplained, Norman started thinking of motorcycles.

A year later a good friend took the carburetor apart and discovered that it had a blowhole through its main jet. The part that was brand new and beyond suspicion was the problem. By then the bike design was becoming interesting and the engine was bypassed.

Fast forward to 2010 and now in the USA Norman dragged all the bits out of their box and put it back together. This time with a more detailed and careful rebuild. Add a new carburetor and this time the performance is much more impressive. The engine now starts and runs well and is installed in a pocket bike to add to the fun. The total run time now probably exceeds 1 hour.

So why do this? What is it for and what are the gains?

  1. Only 2 moving parts.

  2. Only 3 housings.

  3. More compact overall package (for a given engine size the form factor is smaller. It’s why a fridge is square.)
  4. Asymmetric port timing (it’s a 2 stroke). 2 stroke porting is fixed by its position on the cylinder wall. As such the opening and closing happens equal sides of BDC or TDC. This means that there is never a perfect timing, it has to be a compromise. This compromise is one of the reasons we don’t see may 2 stroke engines these days. 2 stroke engines waste a lot of unburnt fuel down the exhaust, and the EPA doesn’t like that. The HOSSACK design changes that because the porting can be positioned to be asymmetric.

  5. Reduced end loads. (Norman does not have the mathematics to prove this but does know that normally a piston changes its direction abruptly at TDC and BDC. On this engine the lobe (piston) takes 40 degrees of crank rotation to change direction at BDC and 25 degrees at TDC.)

  6. Combustion chamber squish. (This is a 2 stroke thing). Early engine design put a lot of effort into swirling the gas in the combustion chamber. This engine does it automatically.

  7. Fun!

Looking to the future. Norman is working on several new ideas for this design and yet another design for the internal structure. The area Norman wants to pursue sets him against the current again. He poses the question - could you make a very small IC engine this way to compete with battery packs? Norman has designed an engine .036cc which he plans to run on butane gas. Yes, there is an emission issue but the energy density is hugely in favor. UAV’s are becoming big news and there are many areas where a lightweight power source could be very useful.

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