But today we are not talking about sales, let’s talk about the line of Mazda engines with the beautiful name SkyActiv. Mazda engines have never been spoken badly, here are the rusting bodies, yes — it was, but everything seems to be fine with the engines.
Since 2012, people began to download information about the new Mazda SkyActiv technology, managers in the salons said: “the compression ratio is like in Formula 1.” (Just in the 13th I bought Rav4, I also considered Mazda CX-5). Simply put, SkyActiv is a new line of current company engines, there is SkyActiv G (gasoline) / D (diesel) / R (rotary engines) / X (gasoline internal combustion engine, with compression ignition as in diesel engines).
We will analyze only SkyActiv G, since the rest is of little relevance to us. In fact, this is a well-modernized old line of Mazda engines. The Japanese, as always, did not dare to simply follow the trodden path of their German colleagues.
The fact is that SkyActive are engines with direct injection such as GDi or FSI. The fuel injector is located directly in the combustion chamber, for sufficient injection pressure, an injection pump (high pressure fuel pump) is used.
What advantages does such a system provide if it is used on a more classic engine, where the nozzles are in the intake manifold?
However, this is far from the only advantage of direct injection and Mazda engineers
SkyActiv has a compression ratio of 14:1, which seems good, but you need to understand that the fuel in the engine should burn, not explode, increasing the compression ratio, we increase the temperature and pressure = detonation, and detonation destroys the engine, because this is not combustion, but explosion.
So, direct injection allows you to use fuel as additional cooling for the cylinder. There is such a “layered injection” mode, fuel is sprayed in a small volume on the intake stroke, spreads through the cylinder and cools it, the second injection occurs on the compression stroke to enrich the mixture. And by cooling the combustion chamber, we reduce the likelihood of detonation.
Instead of the usual “microphone” of detonation, there are ion sensors in the coils that measure the current at the spark plug electrodes and conclude whether there was detonation or not.
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Another trick is the release of 4-2-1, the so-called «spider», this release allows you to remove exhaust gases as quickly as possible, and this also has a good effect on cooling. In addition, it is equal in length, and, therefore, the temperature of the cylinders will be as uniform as possible. The catalyst is far enough away to pass according to euro standards, layered injection is also used, the mixture is as rich as possible, there is a quick warm-up (usually at this moment (20 seconds) the engine is quite noisy).
The tricky Otto-Miller cycle system
Separately, it is worth talking about the phase shifters, there are two of them, for the intake and exhaust camshafts, the classic hydraulic on the exhaust, and the electric on the intake. This is necessary to ensure the operation of the engine according to the Otto-Miller cycle. The essence will be clearly visible in the animation below.
The Otto cycle is classic, it works in the catalyst warm-up mode, medium and high loads. The Miller cycle is used in light load and idle modes. Simply put, in the Miller cycle, the intake valves close with a delay, thereby forcing some of the air back into the intake manifold. This is used to reduce pumping losses, and, consequently, to save fuel in modes where it is not necessary to squeeze the maximum out of the engine.
If you understand that the motor is heat-loaded and prone to detonation, and this = oil is used up faster due to temperature, and AI-92 is not suitable (and the 95th is not particularly, ideally you need Japanese 105). That even despite the lightweight t-shaped piston to pass for SkyActiv 200-300 thousand, the task is quite feasible, but it depends heavily on maintenance and driving style.
The main thing to watch is the chain, fuel, oil. There are situations of sticking of pistons to the walls of cylinders during overheating, destruction of pistons during detonation. In the case of repair according to deshman, you can, of course, try to re-sleeve the cylinders, but if you want to drive for a long time, then it is better to buy a Short block, the price is about 140 thousand.
Of course, there are special cases when people report replacing a short block on runs of 80-90, but most often they are no longer the first owners and it is difficult to judge the mileage.