Some general consideration, especially on future possibilities for the two-stroke engine seeing that karting is remaining its last bastion. Report by Simone Suardi
Changing the topic, (off the cuff remember?), today during one of my rare coffee breaks, after the usual “man talk” we ended up talking about the solutions used in the past, going back to the early nineteen hundreds, and such solutions were sometimes even uncomplicated, but in some cases they had just been thought up at the wrong time in history.
Often, in fact, technology wasn’t ready to develop some ideas brought up by clever designers. In the end it wasn’t just rhetorical saying that, in most cases, someone had already thought of certain things before we did. At least, in the field of motorsport this has proved to be the case, and we have to accept it.
However, after having heard things like “in twenty years time we will probably have to change jobs because everything will be electric”, I came out with, just for a laugh: «Well, probably in ten years time we’ll go back to the two-stroke». As everyone knows, I am a fan of the two-stroke and will be to my dying day, they were my first love, if not I wouldn’t be writing this page, and to be honest I still think that there is a chance and not a remote one either. Everyone can see that nowadays they are, unfortunately, relegated, to only a few sporadic events, not even top ones, even if the level is good, I have nothing against engine tuners, drivers and kart drivers in general, but out of the championships “that count”, the ones that make real money, the 2-stroke have been out for over a decade (MotoGP), in others they haven’t ever even entered and maybe simple due to regulations (Formula 1).
True, you have to start from the bottom, but nowadays the 2-stroke needs a net change and this is only possible where there are resources, lots of recourses, in terms of people, know how and money to invest. It’s no longer the time where an individual who has genius and creativity can actually change things. I think it is an improbable situation, let’s say, with the degree of specialisation required today.
Probably most of you don’t know, and certainly quite a while ago, an Australian firm, Orbital, made a direct injection helped by air, to make up for the brief mixing period, which seemed to work quite well; and not by chance that patent for two-stroke applications, as far as I know, was bought by several important car and motorcycle manufacturing set ups. Always from what I’ve heard, some factories, important ones, already had some small fleets of vehicles powered by 2 stroke injection engines. That period was the same one when diesel started to seriously pick up also out of heavy transport thanks to that simple idea, but at the same time very crafty, it was the very well known common rail. A project that I’d like to underline, has Italian origin, seeing that it was invented inside the Fiat Research Centre. Then everything was sold to Bosch who had the means and the resources to make it work (and on which, in the end, they have made real money from this). The thing is that many factories are at a crossroad: diesel or two-stroke? Without a shadow of a doubt, the first seemed an investment that was less hazardous and I’d say it’s evident which one top managers have opted for. They have done nothing but decided on the direction obviously towards which the market tended for.
The great risk of betting on the 2-stroke could have already been itself the prejudice of people who have the idea that it is an engine that consumes, pollutes and spits oil; in fact the idea itself isn’t really wrong, but from what we have seen today, well... And this is the exact point I wanted to get to: who says that I have to do things like they have always been done using transfer and exhaust ports, lubrication loss and other things?
The thing is that it’s an old idea, which has been left practically the same since Walter Kaaden first came up with the idea of an expansion muffler. Ok, in the meantime there have been changes such as doing away with the old “piston port”, that is, piston controlled induction, and the use of better methods like the lateral rotary disc, reed valve and, in the end, everything was developed to its maximum expression by Aprilia with its front rotary disc RSA 125cc, however, the substance is basically the same. The high specific power two-stroke has always been based on making the most of the pressure waves generated by the expansion muffler to avoid, at least in tuning revs, losing about 50% of the fresh load directly at the exhaust. Let me ask you a question: if you were to think of a new engine, would it seem logical to carry out the induction phase in a way that this is always connected to the exhaust duct? More so if the fuel is introduced before anything else? This means that if there is air loss, we are also losing fuel at the same time! I don’t think so. It’s obvious that this way there will never be a future for a two-stroke engine, because what we get from fluid dynamics at given revs, increasing the transfer phase and “blocking” the exhaust port and putting fuel load into the cylinder again, the fluid dynamics then removes it at other revs, because it does the exact opposite to what we’d like done. In the end, we’re talking about waves that can be controlled only up to a certain point. Among other things, in past issues we mentioned one of the ways commonly used to extend the range of function is to delay advance at high revs: so the hotter gasses are downloaded, because in fact we are moving combustion forward and the exhaust port, which opens always at the same instant will let the combustion process end earlier than usual. Hotter gasses means higher speed sound and, seeing that waves travel at the speed of sound, it’s as if we “fluid dynamically” shortened the muffler tuning the engine for an instant at a higher rev. Shame that removing advance is a way of killing engine efficiency. Generally speaking, we have more horse-power, but they are “worse”. This we talked about in previous issues of the magazine. And then without bearing in mind that for a mass production nowadays you need to have all those things like catalysts, diesel particulated filters (that luckily you don’t have to use on motorbikes yet) and the more you have the better, things that make it absolutely “impossible” for you to make the most of the dynamic of expansion thrust as you have in a two-stroke, to get remarkable power. In simple words, adding all the systems to the exhaust, the muffler would no longer be able to carry out the job that it was at first developed for.
The symptoms for the relatively “scarce” efficiency of the traditional two-stroke engine were also noticed in early 2000 when they raced contemporarily the spectacular 500 cc 2-stroke against the 1000 4-stroke. In theory, the motorbikes that mounted the two-stroke, also lighter, should have had more or less the same level of performance, but it was evident the valve engines were far better. Aprilia then came out with, in lower classes of the world MotoGP, that great project, the RSA and this undoubtedly represented the apex of traditional two-stroke development. Today though, it’s not enough, we have to look to the future.
Imagine if you can’t get the injection to work properly and, which is the first thing to do, maybe taking the idea of the Orbital air assisted injection, because in any case, differently to the 4-stroke, you still have the problem of having very little time for the fuel to mix with the air, without considering the frequency of the same injection. At the same rotation revs as a 2-stroke it has to inject with twice the frequency, as the useful phases are double, but it could also theoretically give twice as much power! I mean, you could think of a configuration with a central spark plug and double injector, or a central injector, lateral spark plug, exhaust valve on head and perimetral induction “from below” through the ports. And if we talk about valves, do they have to be mushroom shaped? They could be spherical/ rotational with a central canal, shaped appropriately to prevent the coefficient of flow from dropping when the canal is no longer coaxial to the flow. Or if there were mushroom shaped, has the lift law got to be done by means of a traditional cam, making it move along the axis going into the cylinder?
These are the first things that come to mind and obviously they are far fetched, because when you really come down to doing it you run into serious difficulties. One thing is sure; changes don’t come about if you do the usual things.
One thing is sure, if we want a “revival” for the two-stroke engine, I think it can no longer be the normal engine that we all love and know as it is. I am among those, I simply love the roar, the smell of the fuel mixture and the incredible weight/power ratio that it can bring about, but, I think we have come to a dead end road, there’s no way out.
I’ve seen that last year Honda deposited a new patent (you can see the pictures included with this article) for a two-stroke fuel injection engine, which isn’t very far from one of the suggestions I made earlier. You can see at the induction a throttle with reed valve after it, if I’m not mistaken, I can see a fuel injector positioned down below, in the casing that “shoots” inside a transfer duct whose port is controlled by the piston. Up to this point, it seems like the 2.0 version of a piston port. At the top we can see the spark plug decentralised and at least an exhaust valve, controlled by a finger that seems to look like a rod that goes to the driveshaft. Well, if this was the case it isn’t all that awesome and I feel like saying that it certainly wasn’t made for motorcycles, or at least for applications where you need great specific power combined with high rotation speed. In any case, something is moving and I really hope that things continue to do so. There has to be someone important who believes in it and puts down a serious investment plan because the way I see it for small applications, that also include small cars, the two stroke has an incredible potential in terms of capability of connecting high performance with weight and very small dimensions. Without forgetting the simplicity of the basic mechanics.
Let’s hope, as I honestly can’t stand hearing those 4-stroke single-cylinder “small tractors” that crowd our streets.
My dear Vroom readers, the title gave advanced notices on all this; we really just talked off the cuff and now I think it’s time to conclude. I will see you again here, maybe next time with something more conventional, what do you think? Don’t worry, I already have some ideas. Rock on guys, see you next month.