Sometimes multiple inventors stumble upon an idea independently of one another. Patent filings and other documentation thus become necessary to determine who has priority. I once came up with an idea and later learned I was thirty years late, but maybe it was a good idea anyway. I recall this because I found something packed away that brought back the story. ….and a few choice words because the memory triggering object was heavy and incompatible with toes.
In high school, one of the classes I took was an engineering design graphics class….sort of an advanced drafting class that added in not just how to represent objects on paper but how to refine the ideas behind them, possibly into something useful. It was taught by Mrs Prater, who is still at the school….likely teaching this and other related classes. Her students typically keep in touch even many years later. (and I will be sending her a link to this story) One of the good teachers of the sort you learn a lot from and remember……..even if you don’t stub your toe on something you made for the class 25 or 30 years before!
So we had an assignment to identify a problem, come up with some preliminary ideas, refine those ideas, analyze, develop, and implement the concept. I decided to tackle something that was within my understanding but far beyond my ability to really implement in a fully developed state. Luckily, the assignment allowed for simply demonstrating that the conceptualized item could be done. I decided to create a new type of internal combustion engine. Yeah, really. You know, give the big three a run for their money. Haha. Right.
What I decided to tackle was the bane of every hot-rodder at the time: knock and ping…..destructive detonation in a high compression engine that will usually result in ruining a powerplant in short order. It is a very real problem that many engineers have spent countless hours trying to address since the first time Otto started his first engine. So naturally I was gonna solve it in just a few weeks. But maybe I did.
Detonation in a cylinder can be caused by a couple of things, most notable are pre-ignition caused when the heat of compression causes the fuel/air mixture to ignite prior to the sparkplug firing the charge….and another situation where the firing of the sparkplug igniting the fuel causes a rapid rise in pressure which then ignites another pocket of fuel within the combustion chamber…..this results in multiple flame fronts colliding and creating shockwaves which are not only hard to model but also can be very destructive. Such conditions can easily blow a hole through a piston or break a cylinder head! The most readily available means to control this aside from higher octane fuel from chemical additives like Tetraethyl Lead are lowering the BMEP (brake mean effective pressure) within the cylinder, which relates to lowering compression ratios and/or boost levels, cooling the fuel-air charge, either by intercooling, water injection, or enriching the mixture or further lowering the pressures. Retarding the ignition timing also helps in terms of temperatures and BMEP conditions. However, all of these things result in a lowering of power produced per pound of fuel burned. Keep in mind, the computer controlled systems we use in cars today to precisely adjust fuel flows and ignition timing in response to changes in load, throttle position, air density, and fuel burn rates simply did not exist when I was in school. The period of 1975 through 1985 (give or take) really was a dark time for American automobiles. In an effort to reduce emissions and increase fuel economy, manufacturers slapped all manner of ill-conceived crap onto what were basically powerplants that had been unchanged since the 60’s and 70’s. The results were mixed, but with very few exceptions they suffered from poor drivability and low performance. Ask any car person and they will almost universally agree that the cars of that period sucked.
In spite of this, both diesel engines and jet turbines run low octane fuels at very high pressures and temperatures without being destroyed. The key is how they burn their fuel. In a four cycle gasoline engine, a mixture of fuel and air (provided by the carburetor or fuel injection system) is drawn in, compressed, ignited and the burning gases expand pushing the piston and doing work, and then the combustion products exhausted. The critical issue with regards to detonation, is the heat and pressure during the compression stroke. Once ignited, the flame front travels across the mixture as it begins to expand and perform its work. This is the key, the flame travels across the fuel.
In a diesel, only air is pulled in and compressed. It is compressed to a much greater ratio and becomes very hot. (remember physics class?) …the compression ratios may be on the order of 20 to 1……whereas a gasoline engine might only run 8 or 9 to 1. At such pressures, the air becomes superheated and when fuel is injected into the cylinder it immediately ignites and expands. Fuel is fed into the flame. The flame front is, to an extent, stationary. In a gas turbine, air is compressed by the compressor stages and then fuel is sprayed in and ignited by a spark…the burning gases then expand out through the “hot section” turbine blades which provide power to turn the compressor section and do other work. Again, the fuel is fed into the fire. The flame front is stationary.
In the diesel and the gas turbine the fuels are very similar. Diesel and Jet-A are somewhat oily and akin to kerosene. While a gas turbine will tolerate gasoline, a diesel will not. Aside from the abrasive nature of gasoline (which would rapidly damage a diesel injection pump) the burn rate is so much faster that if gasoline is injected instead of diesel fuel it burns so fast that it is more like an explosion. Not a good thing in your engine.
So….could the best of both be combined?…could you create a stationary flame front inside of a gasoline fueled engine? …and if you did, could it also burn diesel fuel without damage? …and could it be done with simple, mechanical means? Remember, reliable computer controls in automotive applications were nonexistent back then. Besides, I also chose to come up with something that would work even in a “Mad Max” world.
After kicking around some variations, what I decided needed to be done was to have a high compression (but not as high as a diesel) engine that, like a diesel, only pulled in air on the intake stroke. Then, when compressed, this air needed to be swirling around. Like a miniature cyclone inside of the chamber. This chamber and its mating piston needed to be shaped to create and maintain the swirling flow. In the chamber, I planned to have the usual sparkplug…PLUS an injector. I wanted the injector upstream of the sparkplug. The idea being to feed my fuel into the point of ignition and hopefully, maintain a relatively stationary flame front as the gases expanded and pushed the piston.
All great in concept. But, I was not entirely certain HOW to do this. Nevertheless, the theory sounded good to a 17 year old. For the class, I needed some sort of model. So I was going to mock up a cylinder head and piston to show the idea. Not being the athletic type, I was NOT going to carry an entire cylinder head into class. They get heavy. Especially heads from an early 1950’s Chrysler Hemi V-8. I like old Chrysler products and the hemispherical head engines they made were top notch in terms of power–it seemed a suitable place to begin. …..and, I had a dud head from another project. So I cut one chamber off to make my model. Today, I would never dream of slicing up a vintage hemi head….even a cracked one…..but back then, it was just an old car and nobody would have bothered to repair a cracked head. Today things are different and such an item would be prized and carefully repaired. Cracked or not. This head, became my “flow bench” model that I brought in, along with some other items, for my presentation. This head is also what I found to be incompatible with my toe many years later.
Today the head– complete with material I put on it to shroud the intake valve to hopefully make a swirl, some pencil marking showing where to cut a hole for the injector to be added, and a made up “cyclone series part number” engraved in the side now sits atop my bench on a display shelf.
Obviously a typical high school kid does not have the resources–either machine shop access or finances to construct a full working prototype of something like this, let alone refine it to a production model. But did the idea have merit? Maybe. Maybe not. Or so I had assumed, for a long time.
That is, until I found an old magazine from the early 1950’s. I can’t remember which magazine I first saw it in…likely Popular Mechanics, but maybe Popular Science, Mechanics Illustrated, etc, etc. There were many such publications in the postwar years. America had just fought and won a very technological oriented war and the dawn of computers and spaceflight was upon us. People were excited about science and technology and wanted to learn as much as they could.
What I found in the magazine was an article about the “Texaco Combustion Process” This was a stratified charge engine whose goal was to have multifuel capability, greater efficiency, and a complete resistance to knock regardless of the grade of fuel being burned. Furthermore….this engine used a swirl chamber with an injector placed upstream of the ignitor to have a stationary flame front!!! So….I guess someone thought the concept had merit, even if their specific design to achieve the concept was different than what I was toying with. My study model for class may have been wrong–afterall, I had no flow bench or any way to visualize the real operation……..but the concept was valid at least enough that Texaco apparently built some test engines…a few of which were then fitted to real cars to try them out.
To my knowledge, no such powerplant made it into a production car. Some elements of the concept did, however. Mercedes used a direct injection in the 300SL Gullwing car…..and some diesel engine manufacturers opted for a swirl chamber of one form or another. My suspicion is that the abrasive nature of gasoline would have been very rough on injection pump designs of the day and this was a major roadblock to making a reliable powerplant. In addition, the level of cleanliness needed to avoid clogged injectors would be pretty stringent. Even Mercedes abandoned their direct injected gasoline engines. There may have been other shortcomings to result once one began actually running such a vehicle but those are just the ones that seem obvious to me. Does the concept have merit now? With better materials and control techniques could a new variation of this be refined to a point of being viable for production? Perhaps building upon one of Mazda’s Wankel engines because the rotary sweeping motion would achieve the gas movement needed without trying to engineer a reliable swirl pattern…and those engines already have two sparkplugs per chamber–one of which can be removed and replaced with an injector. As this is a mass-produced item, the cost to get one to play with would be much lower than building something totally from scratch. Had I known this idea was going to resurface in my life I would probably have kept my old RX-7….it was a lot of fun to drive anyway.
Sometimes stubbing your toe can provide an interesting mental exercise…..after you get past the choice words you have to say about it.