Today a netizen in one of my articles (double cycle, double spray, double boost what does it mean?) What are the advantages of these technologies? Comment below, what does the "intake harmonic boost" mentioned in the article mean? First time hearing about this concept. I thought that this concept is not explained clearly in one or two sentences, and this should be a blind spot for many people's knowledge, so simply write an article to explain it.
As we all know, many cars are now equipped with supercharged engines, that is, using a supercharger to press more air into the engine combustion chamber, and then injecting more fuel, you can achieve the effect of small displacement output and large power. These engines, without exception, have a supercharger, either a turbocharger, a supercharger, or both. For engines without any superchargers, we call them "naturally aspirated engines." This engine power is not as fierce as the supercharged engine, so many people think that the supercharged engine technology is more advanced, in fact, this view is very one-sided, "supercharging" and "natural intake" is not the standard for judging whether the engine is advanced or not, just like dumplings are delicious and not on the skin.
Since it is a "natural intake", the outside air is sucked into the combustion chamber by the engine, rather than being pressed into it, so the amount of air entering is limited, and the power of the engine is limited. In order to let more air enter the engine, automotive engineers carefully studied the process and path of air entering the engine, and finally discovered the characteristics and laws of the intake air, designed the "intake harmonic boost" system, and realized the "intake pressure without supercharger".
The working principle of the intake harmonic booster system is mainly to use the inertia of the inlet air flow to increase the pressure.
For naturally aspirated engines, the process of air entering the engine is not continuous, but intermittent and cyclical. When a cylinder starts the intake stroke, the intake valve opens, and the air enters the combustion chamber at high speed through the intake valve; when the intake stroke ends, the intake valve closes rapidly, and the air flowing at high speed near the intake valve is suddenly blocked, stops flowing, and will form a certain pressure outside the intake valve, and rebound in the opposite direction, forming an air wave oscillation, which is the so-called "harmonic". The principle of formation of "water hammer" in hydraulic systems is basically the same.
Harmonics propagate and reciprocate at the speed of sound in the intake pipe, and if we do not control it, it will repeatedly reflect oscillations in the intake pipe, forming turbulence, which in turn affects the intake efficiency of other cylinders and reduces the engine inflation coefficient. If we can design a structure that controls the direction and frequency of the harmonic oscillation in the intake pipe, so that the harmonic oscillation frequency coincides with the opening and closing moment of the intake valve, so that the reflected pressure wave is concentrated just near the intake valve that will be opened. In this way, when the intake valve is opened, the air will actively enter the combustion chamber, not completely inhaled, and the intake pressure will be greater than when the natural inhalation is made, thus forming an intake pressurization effect.
This intake structure is called "intake harmonic boosting", which is a naturally aspirated engine that uses the movement inertia of the intake air to produce a supercharging effect, and is a natural supercharging system. This technology is now used in almost all naturally aspirated engines. Its main advantage is that there are no moving parts, reliable work, low cost; the disadvantage is that the supercharging effect is limited, generally only allow the engine to enter 10 to 20% more air, the engine power improvement effect is not obvious; in addition, because the pressure and frequency of the engine intake system are fluctuating at any time, so the intake harmonic supercharging can only increase the intake volume and engine torque at a specific speed, and cannot achieve the intake pressure at full speed.
The main structure of the intake harmonic boosting system is to set up a resonant cavity (or power cavity) in the intake duct, in which the air forms a harmonic oscillation to produce an intake boost effect. The size and shape of this resonator are related to the displacement of the engine, the number of cylinders, the cylinder layout type, etc., which looks like a simple empty shell, but in fact, the technical content is very high.
Interestingly, some turbocharged engines also have resonant chambers. For example, Volkswagen's 1.4TSI engine has three cylinders of different lengths arranged side by side on the intake pipe, which is also a resonant cavity. Of course, its main role is not to use the intake pressure, but to balance the pressure fluctuations in the intake pipe, to avoid the change in the throttle opening, the pressure change in the intake pipe is too large, causing engine shaking or driving setbacks.
Now there are also some natural intake engines, using variable length intake manifold technology, such as Toyota's ACIS, BMW's DISA, Audi variable intake manifold, etc., which are also an intake harmonic boosting technology. They use the ECU to control the opening and closing of the solenoid valve in the resonator, control the opening of the flap, and change the length of the intake pipe. When the engine is at a low speed, the effect of low speed torque is achieved through a longer intake manifold; when the engine is at a medium and high speed, the intake volume of the engine is increased by a shorter intake manifold, thereby obtaining a more powerful acceleration capability. This ECU-controlled intake system is also known as the Intelligent Harmonic Booster Intake System.