The birth of Pulse Jet Ignition
Words by Steve Scriminger,
During the development in 2001 of the iconic BMW air cooled R-series engine for aviation use, we encountered a number of problems that weren't apparent in the motorcycle it was manufactured for. The first was cooling, in an aero engine we measure cylinder head temperatures and exhaust gas temperatures, this gives early warning to impending doom, which is necessary due to the lack of lay-by's at 3,000ft! We found that if the engine was held at BMW's quoted max continuos rpm of 7,000, the C.H.T.'s just went up and up, even with a 68inch 3-blade prop as a cooling fan! In addition to the C.H.T.'s climbing, so did the E.G.T.'s, exceeding the valve manufactures recommended limit of 750c.
The C.H.T's were cured by not blowing air at the engine, but by drawing it over the engine. The act of blowing air (compressing it) heats it up reducing the cooling ratio, however by drawing it off the back(expanding it) this cools the air, increases the cooling ratio and makes for more efficient cooling. The E.G.T.'s however were a problem. We altered the valve timing to hold the exhaust valve closed longer, this had little effect apart from reducing output. It was at this point we noticed that exhaust valve seat recession was also a problem, being exaggerated by the high temperatures.
After a bottle of Red and some cheese, we decided that we were treating the symptom not the cause, the cause being too much flame leaving the cylinder when the exhaust valve was open, which must be down to an incomplete burn.
The first modification we tried was to twin spark the cylinder heads, this gave an improvement in performance and reduced the E.G.T's, but not by enough, back to the drawing board. Our conclusion was that there wasn't enough T.D.C. turbulence (squish) to propagate the flame, we increased this which also had a benefit, but not enough. The problem with squish as a flame propagator is that the spark initiates the burn some 30 degrees before T.D.C.
There had to be a better way, Steve then remembered the old chineese proverb "Man with fire stick on hand, burn hand, Man with fire stick in clenched fist blows hand off". The Pulse -Jet Ignition was born, a small pre-combustion chamber where a small percentage of the cylinder charge is ignited with a spark, the resultant explosion from the ports of the pre-combustion chamber causes multiple flame fronts and huge amounts of turbulence at the point of ignition.
The patented P.J.I. is designed in such away that the differing port volumes creates a low pressure after the explosion, drawing in any unburnt fuel and air, as in a pulse jet.
We have tested a large number of difference design and patterns in past 10 years before we've reached the final design that we are offering you today.
Pulse Jet Ignition is a product of hard work and dedication of Mr. Steve Scriminger of Scriminger Engine Developments. Sinroja Motorcycles is proud to be bringing it to the masses with help and guidance of Steve.
INVENTED, DESIGNED AND MANUFACTURED IN LINCOLNSHIRE, ENGLAND.