Why Do Diesel Engines Use Air Flow Meters and Throttles If Fuel Amount Is Controlled?

Hello.
In cars with a compression-ignition engine, we control the amount of fuel, not the fuel-air mixture, as it is in "gasoline vehicles". The amount of air drawn in is constant. I wonder why a flow meter is installed in diesels. Since the amount of air is constant, why measure it? Is it related to the turbocharging commonly used in this type of engine? The same is with the throttle. Since we control the dose, why the possibility of air control? Heard it has to do with ERG.

And why such a stupid idea that the amount of air is constant? Even in naturally aspirated engines, this changes along with the changing condition of the engine, or someone tries to fix something in the exhaust and immediately the wave effect ... shoots.

ociz wrote:

And why such a stupid idea that the amount of air is constant? Even in naturally aspirated engines, this changes along with the changing condition of the engine, or someone tries to fix something in the exhaust and immediately the wave effect ... shoots.

You must have had a fancy with this condition of the engine! So, following your course, the driver should have coded that after 100,000 km, the parameters should change after 250 the same ... nonsense. There is the same amount of air, even if it is turbo, it is a pressure and temperature sensor, so knowing the pressure and temperature, a clever controller knows what the density is and will calculate the mass. So what's the point for? Good question and the answer is simple too

Well, not so exactly, especially in supercharged engines, where the intake manifold is often stuck with rubbish.

We are listening, what is the flow for?

amm212 - have you ever heard something about self-adaptation for this example? I am very curious about your simple answer. I'm looking forward.

amm212 wrote:

ociz wrote:

And why such a stupid idea that the amount of air is constant? Even in naturally aspirated engines, this changes along with the changing condition of the engine, or someone tries to fix something in the exhaust and immediately the wave effect ... shoots.

You must have had a fancy with this condition of the engine! So, following your course, the driver should have coded that after 100,000 km, the parameters should change after 250 the same ... nonsense. There is the same amount of air, even if it is turbo, it is a pressure and temperature sensor, so knowing the pressure and temperature, a clever controller knows what the density is and will calculate the mass. So what's the point for? Good question and the answer is simple too

There is the same amount of air, even with turbo, and if you want to calculate the mass of air, knowing only the temperature and pressure - it took you away! They used to be flow meters, but they had a problem because they did not measure accurately (the influence of temperature on air density). In the case of hot air, volume It was constant and the mass fell down. That's why we now have mass meters, thermal and ultra. In sdi there is no flow because this engine has a constant mass of air for e.g. 1.9l for a full cycle. With turbo the situation is changing, there are no fixed values , and for precise dosing of fuel in relation to the sucked in, compressed mass and at a specified temperature, these devices are used, i.e. a 1.9-liter turbocharged engine can suck 2 liters of air for a complete cycle by means of a compressor, or rather a mass corresponding to a normal pressure of 2 liters.

Let's just add that there are quite a few supercharged engines without an intake air temperature sensor. In newer ones, where its influence on control is negligible, corrections are minimal. A little bigger in the CR. I know what the answer will be, there has already been such a discussion ...

tomek.kopiec wrote:

amm212 wrote:

ociz wrote:

And why such a stupid idea that the amount of air is constant? Even in naturally aspirated engines, this changes along with the changing condition of the engine, or someone tries to fix something in the exhaust and immediately the wave effect ... shoots.

You must have had a fancy with this condition of the engine! So, following your course, the driver should have coded that after 100,000 km, the parameters should change after 250 the same ... nonsense. There is the same amount of air, even if it is turbo, it is a pressure and temperature sensor, so knowing the pressure and temperature, a clever controller knows what the density is and will calculate the mass. So what's the point for? Good question and the answer is simple too

There is the same amount of air, even with turbo, and if you want to calculate the mass of air, knowing only the temperature and pressure - it took you away! They used to be flow meters, but they had a problem because they did not measure accurately (the influence of temperature on air density). In the case of hot air, volume It was constant and the mass fell down. That's why we now have mass meters, thermal and ultra. In sdi there is no flow because this engine has a constant mass of air for e.g. 1.9l for a full cycle. With turbo the situation is changing, there are no fixed values , and for precise dosing of fuel in relation to sucked in and compressed mass, these devices are used, i.e. a 1.9-liter turbocharged engine can suck 2 liters of air for a complete cycle, or rather a mass corresponding to a normal pressure of 2 liters.

Of course, knowing the pressure (vacuum) in the intake manifold and the temperature can measure the mass. The speed in the collector and thus the air volume is measured by a vacuum sensor, which is then converted in terms of temperature thanks to a temperature sensor, which allows you to obtain a mass amount of air.

What kind of diesel vacuum sensor are you writing about?

I only referred to the sentence

Quote:

if you want to count the mass of air, knowing only the temperature and pressure - it took you away!

So, in general, the flow meter (mass measurement) is used to make the engine speed independent of external factors such as ambient temperature or pressure, so that the speed control is performed only by means of the gas pedal?

"Of course, knowing the pressure (negative pressure) in the intake manifold and the temperature, you can measure the mass. The speed in the manifold and thus the air volume is measured by a vacuum sensor, which is then converted in terms of temperature thanks to the temperature sensor, which allows you to get a mass amount of air."
Yes, in theory, and here my colleague RB26DETT put it very well that many factors affect the calculation of the dose for the engine, and that's what I meant. The pressure and temperature alone are not enough for a turbo supercharged engine. only air and fuel, but for the efficient, economical and ecological operation of the diesel engine, many more factors are needed, the management of which is possible thanks to today's technology.

tomek.kopiec wrote:

Pressure and temperature alone are not enough for a turbo-charged engine.

maybe not so completely, because the Iveco Tector engines in terms of measuring the amount of air have only a temperature and pressure sensor and somehow work (euro 3 if I'm not mistaken) they are Common Rail but maybe they are not so modern

But that doesn't prove anything, if you insist, you can make a CR without any sensors. Well, maybe not without a gas pedal sensor. Again, what I don't like here starts. Academic discussion and we still do not even know what engine we are talking about.

"barubar" refers to a diesel engine

I can see that the discussion is getting interesting and, on the other hand, I am sorry. or even mournfully that so many stout professional heads who can mock someone who, for example, is a cook and will answer a seemingly simple question for them and cannot answer an elementary question ... .

I consider the topic to be explained, but I have one more question, as Barubar called it "academic". I always wonder what is the point of installing turbochargers in gasoline engines where, of course, the main obstacle to increasing the compression ratio and pressure is the knocking phenomenon?

Therefore, turbocharged gasoline engines are "relaxed", ie the compression ratio is lower than in naturally aspirated engines. Does this answer satisfy you?

barubar wrote:

Therefore, turbocharged gasoline engines are "relaxed", ie the compression ratio is lower than in naturally aspirated engines. Does this answer satisfy you?

Dear friend - relaxing the engine is a simultaneous increase in the capacity of the combustion chamber and, theoretically, the displacement - it is simply easier to stuff a larger amount of the mixture into a larger combustion chamber with less pressure. Knocking combustion again consists of several factors - the degree of compression of the mixture, i.e. its pressure at the moment of ignition, temperature in the cylinder, the moment of ignition, i.e. KWZ, and probably most importantly, the composition of the mixture and the octane number of the fuel, the speed of the flame front depends on the amount of fuel - too a small one will cause the mixture to burn out in the manifold, too large a knock on the walls of the combustion chamber - i.e. detonation combustion - instead of a gentle increase in pressure - that is why gasoline engines require powerful air coolers, often with forced cooling, mixture enrichment, to supply the turbine, blow-off systems releasing excess pressure from the system. It's like that in the "head".

Added after 5 [minutes]:

RB26DETT wrote:

This problem is artificially created by Polish books duplicated since the 1960s. It is not a problem to see a 3.0 engine with a power of, for example, 800KM at slightly higher revs and a boost pressure of over 2.5 bar (2.5 bar on an absolute scale of 3.5). One of the cars leaves the factory in version 2.0> 400KM, compression ratio 8.5 (in the weaker version> 350KM compression ratio 8.8) and somehow there are no problems with knocking

A colleague forgot to mention that these engines work on a mixture that is far from stoichiometric - the fuel is dosed much more than necessary (engine efficiency> 20%) - once due to the "turbine power supply" alone, two due to the elimination of detonation combustion - additional cooling mixtures by evaporating fuel. I will not mention the injection and phase ignition technologies.

RB26DETT wrote:

robokop wrote:

I will not mention the injection and phase ignition technologies.

And something more about it?

This is an apropos of the above considerations - read what diesels do with multi-phase injection, or two candles in the cylinder of petrol engines.

In CR only on idle? What are you writing about? I understand that you have such a Lancer and you checked yourself, is there one fuel injection and one spark for one compression and exhaust stroke?

1. You have no idea about CR.
2. You have no idea about the so-called stratification of the mixture.
3. You have no idea what you are writing about.
4. Good night.

Speaking of relaxing, I found it while reading articles and statements on the forum, this is the explanation:

- relaxation is a larger combustion chamber
- a larger combustion chamber is a larger capacity that will be filled by the fuel-air mixture
- with larger capacity, it is easier to blow more air without using extreme pressures, which puts less strain on the entire equipment
- more air blown allows you to pour more fuel
- a lot of thoroughly burnt fuel is a big kick

Anyone had experience with relaxing and fitting a naturally aspirated turbo? Any opinions on this?

As for the layering of the mixture, he provides the link:
http://www.diaaut.home.pl/r21021c1.htm