Technique: Mazda’s SKYACTIV-G

Posted on 10-07-2016 at 17:58 by MauritsH – 21 Comments”

The term SKYACTIV (hereafter simply with small letters) is regularly passed on AB. What is it, how does it work and what did you do?

The compression ratio

Before we proceed to explanation of Skyactiv-G (the benzinevariant), first, a word in advance. The compression ratio in this story is central. We can be there in a manner of speaking an entire article to dedicate, but for now it is sufficient explanation that the compression ratio is the ratio between the largest and smallest possible space in the combustion chamber is referred to. In other words, the compression ratio, you can more or less read the extent to which the mixture of air and atomised fuel is compressed by the piston before the spark plug ensures that the quantity of combustible.

Bargaining for the pro’s

Bargaining

By that ignition put the mixture of air and fuel. That’s also the reason that the piston will be pressed downwards during the arbeidsslag. Furthermore, it is important to remember. The higher the compression ratio, the more efficient the combustion is progressing. That’s simply expressed, but it covers the cargo. Quite a fitting of the compression ratio, however, brings the necessary risks with it. At a given time is the quantity to be hot and the engine can go bargaining. That means that the mixture ignites spontaneously (at the wrong time) and da’s very harmful for the block. Gasoline with a high octane number (ron) (Super 98, for example) could provide a solution to bargaining (or ‘knock’), but also with expensive peut is the elongation at a given moment. As said before, can beat lead to serious damage to the block. See the picture above.

Most petrol cars with atmospheric engines have a compression ratio of between 10:1 and 12:1. Of course, there are many examples with a higher or lower ratio, but it can’t hurt to get an average to hold for the reference system. We love it so here in 11:1.

How Mazda the compression ratio on the can screws to 14:1

Mazda has a convenient solution is found for the compression ratio to be able to screws without the chance of knock to increase. Here is the role of exhaust gases of interest. We are going to explain this a little out of a four-in-line. There is some overlap between the times at which the exhaust valves of the various cylinders are open. In the case of a L4 for example, cylinders 3 and 1. Because of the overlap with a small part of the exhaust gas of the cylinder 3 back into cylinder 1. In itself not a disaster, were it not that these exhaust gases can be very determining for the temperature in the combustion chamber. It is indeed true in this regard, “the less the better”. Exhaust gases may temperatures reach 750 degrees. The air entering the cylinder through the inlet valves reach a temperature of around 25 degrees. You understand that even the smallest glimmer of the exhaust gas large influence on the temperature in the combustion chamber.

The main element of the Skyactiv-G system is the manifold. In most cases, the L4’s a 4-in-1 setup. The exhaust gases of the four cylinders is coming through an open connection into one exhaust pipe, which makes the risk of exhaust gases of another cylinder in crawling is enlarged. Mazda fits simply a 4-into-2-into-1 system, so that the exhaust fumes simply less opportunity to back a different combustion chamber. Therefore, the temperature in the combustion chambers and reduced the compression ratio to be increased. The picture below makes it clear how the manifold contributes to the favorable temperature management.

As you can see, the exhaust of cylinder 3, there is a lot more to cylinder 1 to reach. Despite the fact that the exhaust valves of both cylinder a certain degree of overlap to get the hot exhaust so less likely to have a different combustion chamber.

Problems in the context of the 4-2-1 manifold and the solution thereof

Of course, the use of a longer intake manifold problems. The exhaust gases get by the excess buizenwerk more space to cool off. In itself is not bad, but the catalyst works better as the exhaust gases hotter. Mazda solves this (very brief) on the inflammation-something to slow down and as the temperature of the exhaust gases to increase. Does the effect of the manifold so partly. In combination with the timing of the ignition, Mazda use of pistons with a separate form. In addition, the injectors with multiple holes for a “better” combustion. These are the main ways in which Mazda and the risk of knock is reduced and ensures that the exhaust gases hot enough for the catalytic converter, but there are more.

Conclusion

The fitting of the compression ratio brings risks in bargaining with them. Mazda overcomes these risks by the exhaust manifold to adjust, so hot exhaust gases are less likely to be in a different combustion chamber to increase the temperature up. Then, apply the Japanese techniques to ensure that the exhaust gases hot enough for the catalytic converter. The gases get by the longer manifold, indeed, more chance to cool off.