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How the H2 range centrifugal compressor works

24 mayo, 2021
descompresor 2

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If we talk about cars or industrial vehicles, today we find turbochargers or volumetric compressors everywhere. But in the world of two wheels it is a rarity which was experimented on commercial models by the four Japanese brands (and by Morini) in the early eighties.

Much earlier by other manufacturers; In the early decades of the twentieth century, we saw many experiments that relied on supercharging, albeit experimentally.

But to this day, nobody except Kawasaki with the H2 and H2R from 2015, and the H2 SX that we debut this season, it has other supercharged models, if we discount the motorcycles that receive a minimum excess pressure from the air that their engines breathe at high speed based on forced dynamic intakes (the systems known as Ram Air).

descompresor 4The physical principle on which they are based is the following: every atmospheric combustion engine reaches a certain power limit that will not be exceeded unless a series of specific factors are altered. The main one is the amount of fuel being burned inside: the more we burn, the higher power figures, of course.

But if we do not manage to increase the amount of air that can be sucked in from its intake, it is absurd to add more fuel. It simply will not burn, because the ideal mixture of air and gasoline, which is called stoichiometric, is that of 14.7 grams of air for each gram of gasoline. If we work close to that value, the performance will be optimal.

Thus, if we manage to get a greater flow of air than that which the engine can draw from the atmosphere by itself, due to the depression created in the intake by its own operation, we can inject more gasoline. On paper it seems easy, right?

More air, more fuel

Thus, if we increase the amount of air with whatever device, we will need an injection that can increase the amount of injection, but always in the right proportion so that the mixture is never lean (too much air) or rich (too much fuel).

But going back to the systems used to increase the air flow, mechanical systems are usually turbochargers (turbines driven by the exhaust gases of the engine itself), or mechanical compressors (pressurization devices moved by moving parts connected to the engine itself).

The first systems, those experimented in the eighties, work by releasing pressure when it has already built up, so that sometimes they create delay in the response or abruptness. So, we don’t fancy ideal for motorcycle engines, despite being very popular in the automotive industry.

As for compressors, most of the employees today are divided into two large groups: the volumetric and the centrifugal. The former, of which there are multiple types, are essentially air pumps that, at each turn, compress a certain amount of air.

descompresor 1Centrifugal compressors, on the other hand, are very similar to a turbocharger in the sense that are based on a turbine (the compressor itself) that rotates inside a shell, so that they do not drive a fixed amount of air, but variable depending on the rotation speed and the air sucked in.

The turbine is driven by a group of gears that multiplies its speed of rotation, up to values ​​that, when explained to those who know them for the first time, usually look like: A) you lie or exaggerate, or from: B) you must have added an extra zero by mistake… Well no, the compressor turbine of an H2, for example, reaches a maximum overpressure of 2.4 bar at 14,000 rpm, while the multiplier gears make the turbine blades rotate 9.2 times faster than the crankshaft . Thus, at 10,000 rpm, the turbine rotates at 92,000 rpm, and at 14,000, its maximum ceiling, at no less than almost 130,000 …

Both the compressor and the corresponding crankshaft coupling gears (driven by an intermediate chain) were developed by the Kawasaki Turbine Department Heavy Industries, given the experience with these systems acquired in other fields of the industry.

It is located behind the cylinders and strategically designed so that the use of an added cooling system is not required to cool the air to be drawn in. Because this type of centrifugal compressors, if they are properly designed, generate much less temperature than volumetric and, above all, that the turbochargers.

In these cases, a extra cooling system for the air, known as intercoolers. Even so, there are many little tricks scattered throughout the bike designed to help improve cooling. The intake box is made of aluminum (much stiffer to support aspiration without warping, but also to dissipate calories).

Another trick: the injectors atomise the gasoline on steel plates and coolant circulation channels have been arranged even around the spark plugs. As for the lubrication of the compressor, it is carried out by means of the oil of the central crankcase, where 35% more lubricant fits compared to the engine in a ZX-10R, for example.

Question of the future

Kawasaki has already produced three models with centrifugal compressor: a 100% performance motorcycle only for the circuit, a super sports car approved for the road and a high-flying sport-touring car.

We know that both the green firm and other Japanese brands are investigating the way to adapt compressors to medium displacement engines, so that a phenomenon similar to the famous “downsizing” that has been experienced in recent years in terms of automobiles can occur.

There, turbos and low-pressure blower compressors have begun to be democratized to feed engines of less and less displacement (and number of cylinders), in search of reducing consumption, emissions and taxes.

In the case of the two wheels, this measure can be optimal because the weight of the set always plays in very favorable ratios. A 1,700 kg car with a 1,200 cc turbocharged engine ends up, in practice, spending much more than promised on the road due to the demands to which it is subjected, using many revolutions per minute and constant changes to achieve that accelerate or recover with dignity.

What offers 125 or more CV, like a 1.6 or a 1.8 equivalent from years ago? Yes but what moves the weight of a vehicle is, after all, the engine torque, and not the power. But motorcycles, with ratios between weight and power not reached in any other vehicle of series, can end up having small displacement engines with the extra thrust offered by a turbo, or any type of compressor, managed by the efficient electronics that are applied today. nowadays to any motorcycle, running the same as with double the displacement and spending considerably less. Something tells us that we will see it shortly

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