the control of the diesel engine
A brief guide to the control ECU of a diesel engine.
To control a modern diesel engine ? need to check:
Quantity? fuel injected
Advance Injection
Duration Injection
In order to control the injection of fuel ? need to know how much air is flowing into the engine and ? need to know the speed? of the engine.
In order to have the 5 factors that are closely connected.
Mass air flow (MAF)
Quantity? fuel injected
Advance Injection
Duration Injection
Speed? of the engine (rpm)
These factors are controlled by the accelerator pedal through the engine ecu.
The pedals electronic send a signal to the controller, which shows how much the driver is pushing the pedal.
The measure ? usually a percentage.
0% does not ? crushed so that the engine idles. 100% ? completely crushed.
Cos? 0% "choking us" the injectors to give a deal? fixed fuel, for a time determined by a fixed time. There? results in a fixed regime to a minimum. for example, 800 rpm. Cos? the idle speed ? been mapped to a specific value for the maf,quantity,duration and advance.
100% of the gas the injectors must give a deal? fixed fuel, for a time determined by a fixed time. Then at 100% throttle ? been mapped to a specific value for the MAF, quantity, duration and advance.
This means that any other percentage of from 1% to 99% will have? also be mapped to a specific value for the MAF, quantity, duration and advance.
Understand the facts and figures. (Based on engine 1.9 TDI PD VAG.)
AIR CONTROL
There ? no control air really in a diesel engine!
This is because the engine has a capacity? 1.9 litres or 1900 cubic centimeters (cm3 ).
The exact figure ? really? 1.897 cm3.
The engine ? a four-cylinder so that each cylinder ? 474 cm3 . (1897/4)
All four cylinders are identical, we only need to "deal" with one to simplify.
If a cylinder has a volume of 474 cm3,the amount? maximum of air and fuel that can? contain ? 474 cm3.
If we ignore the fuel for a moment, and also the volumetric efficiencies,means that the maximum amount? air the cylinder can? contain ? 474 cm3
If the air was a liquid, life would be easy. The quantity? of a liquid that you put in 474 cm3 ? 474 cm3.
The Air ? a gas, and then pu? "adapt to different quantity?" of the air in the same space, depending on pressure, temperature and density.
Cos? how much air you put in 474 cm3 of nonstro cylinder?
This ? determined by the density? of the air, and the density? of air depends on the ambient temperature and pressure.
The density? air ****llo of the sea, and on a hot day,say 20? C ? between 1milligrammmo/cm3 and 1.2 mg/cm3.
And 'pi? easy to think that it is 1.0 mg/cm3.
Cos? 474 cm3 of a cylinder contain? 474x1,0 mg of air, which ? 474 mg.
Cos? each stroke of the piston aspirareranno 474 mg of air. This ? referred to as 474 mg/stroke.
The engine or the ecu does not need to measure this data, why? this ? you get without trying.
Then why? the engine has a mass flow meter of air when you s? that being vacuumed 474mg/corsa air flow mass?
The MAF or (air mass meter) ? a means for the ecu to measure the exhaust gas recirculation (EGR).
The way pi? simple to measure the EGR flow ? to measure,through the MAF,the flow aspirated by the engine.
The ECU knows that the engine is sucking in 474mg/race we have said, then the measurement MAF must be 474mg/travel.But if the measurement MAF for? drops to 274mg/run while it must be still to 474 mg/stroke... where are the other 200 mg/stroke?
The other 200 mg/stroke "come" from the EGR valve as a gas of exhaust gas recirculation.
Therefore, the motor 200 mg/EGR/stroke + 274 mg/MAF/race sucked for a total of 474 mg/stroke.
Then, the control unit "knows" that the MAF should be 474 mg/stroke without the exhaust gas recirculation. (EGR valve) and less than 474 mg/stroke with the EGR valve open.
Then, if the digit MAF remains constantly high (close to 474 mg/stroke), the EGR valve ? stuck closed.
If the digit MAF remains constantly low (near 274 mg/stroke), the EGR valve ? locked open.
Then why? the engine has this EGR valve.
EGR helps to reduce oxides of nitrogen (NOx) which pollute the atmosphere.
The 474mg/stroke of air contains more? oxygen as the fuel pu? burn.
When the fuel consumption ? finished a part of the exhaust gas produced reacts with oxygen ****** that renderono oxides of nitrogen.
This problem can? be reduced by reducing the amount? oxygen 474 mg/stroke of air.
The way pi? simple to do that ? to have less air.
The way pi? easy to have less air ? to add exhaust gas.
That's why? it has a EGR valve and a MAF sensor.
PRESSURE CONTROL OF THE AIR - TURBOCHARGERS.
The pressure of the air and its temperature varies depending on where you live in the world,climate, humidity,altitude,etc...
The following assumes an air temperature of about 20? C has a pressure of 1000 millibars (mbar).
Suppose now that the cylinders receive air at a pressure of 1000 mbar and a temperature of 20? C at a flow of 474 mg/stroke. (To simplify things, we assume that the EGR is not ? involved)
A typical value of the boost of the turbo ? to add an extra 1000 - 1500 mbar of air pressure. Cos? a typical graph of pressure boost against rpm will run you? from 1000 mbar (without amplification of boost) up to 2500 mbar of boost max.
(Then the turbo "pushes" 1500 mbar)
The pressure of the air in the pi?,so if we have 474 mg of air at 1000 mbar can we have 948 mg of extra air to 2000 mbar. Then, with the air we have a pitch twice as high pi? pressure in the cylinder and pu? burn double the fuel much more efficiently than before.
The result ? the engine develops more? power.
You need to? check the turbo as the engine design pu? only withstand certain ****lli boost and this is through the MAP that informs the ecu of a certain ****llo boost.
The engine or the ecu has a sensor boost pressure on the manifold, said absolute pressure sensor (MAP) sensor intake air temperature (IAT).
These sensors allow the ecu to compare the actual pressure of the boost through the MAP, and to correlate the signal with the boost that is stored in the map ECU.
The control unit also has a single value Boost Limiter (SVBL), which acts as an emergency situation by cutting the boost in the case in which this portfolio? reached ? passed.
A MAP turbo will be? used by the ecu to increase the amount? injection in-line with the major thrust.
Another map turbo compares the actual increase of the boost(map sensor) with the increase in need of the boost to the achievement of a given pressure turbo. (BOOST LIMITER)
The effective thrust of the turbo must follow the approximate shape of the map turbo.
If the effective thrust is still too high or too low, the ecu v? in the recovery.
The recovery is active even if the effective thrust exceeds the single value Boost Limiter. (SVBL).
the control of the diesel engine: the control of the diesel.
THE CONTROL OF THE DIESEL
As we mentioned in the previous guide diesel engines aspiranno always the maximum of the air at the disposal of the net dell volumetric efficiencies.
Then the diesel engines do not control their "air intake" through a butterfly valve as the gas but the engine must be controlled by the injected fuel.
Not ? possible to suck the fuel to a diesel,as it happens in gasoline engines why? the diesel fuel must be inserted when the cylinder has crushed the air. Cos? the diesel fuel is injected into the cylinder.
The pressure and the temperature of the air in the cylinder ? very high (at the end of the crushing) so that the fuel must be injected at high pressure.
then:
The ECU knows how much fuel to inject why? he knows how much air is c'? in the cylinder.
and this jargon is called a "deal? fuel injection" (for the deal).
previously we said that in the engine taken into consideration(vw1.9 tdi pd), The cylinder contains 474 mg of air.The Diesel burns in order to achieve the best performance with about a 14.6 mg of air per 1 gram of fuel. Then, 474 mg of air to burn efficiently 32.5 mg of diesel. (474 / jn 14: 6)
This does not mean that the injectors inject 32.5 mg of fuel per stroke (mg / stroke).
32.5 mg / stroke ? the ideal maximum, assuming a normal power supply air and respecting a given Air Fuel ratio(air-fuel)
If the injectors to inject more? 32.5 mg / stroke, part of the fuel does not burn? properly and get? of the engine as black smoke. (This ? often described as the limit of smoke).
The injectors can inject any amount? less fuel to 32.5 mg / stroke and this ? what they are doing.
At idle the injectors can inject ir? or less than 6.0 mg / stroke of fuel.
To increase the speed? the engine will increase? the quantity? injection diesel
The quantity? injection ? controlled by a map in the ecu. The driver wish for the speed? the engine in the pi? ? controlled by the accelerator pedal.
At a minimum, the accelerator pedal is set to 0%, so that no injection EXTRA you will prove?.
When ? fully depressed (at full throttle) the accelerator pedal will be? hold 100%.
Then, the ECU receives a signal that varies between 0% and 100%.
If you press the 30% of the accelerator pedal and the ecu see the maps driver wish, and controls the amount? necessary injection and injects that amount.
simple.
Unfortunately, this is not ? just cos? simple, because the diesel engines in the real world? do not measure the quantity? of fuel that is injected, "downstream of the injectors.the ecu is algorithmic calculations "upstream" but really? the fuel injection ? very complicated,and then this ? an explanation is made very simply.
Imagine a fuel injector such as a syringe loaded with 100 mg of fuel.
The driver presses the accelerator pedal to 30%. The ecu see the maps driver's wish and decides to inject 16 mg of fuel.simple enough...
BUT...When injecting the fuel? and especially for how long the injection should last?
The engine designers misurarano the time of the duration of injection in degrees of rotation of the motor shaft. ? why he feels the people that f? reference to the ignition timing of the engine.
The ideal point to inject the fuel ? generally regarded as the top dead point. This ? the point where both valves are normally closed and the air ? was crushed to the maximum.
TDC ? often referred to as a "time window" in degrees in advance of top dead center (TDC) or in degrees after top dead center. Both are the same,they are just the opposite of the other.
Then 4? BTDC ? the same thing that of -4? from the PMS. ( we will use only BTDC here)
coming back to life to inject 16mg of fuel you will require? a certain amount of time (duration ' racing machines) and why? the piston is going up and down, ? need a point of BEGINNING OF INJECTION.(when we were talking about)
Suppose now that 2mg of fuel to be injected in 1 degree of rotation of the motor shaft (? degrees radial)
Assuming that the best time of injection ? 0? at TDC and 16mg is avr? need 8? duration
the injection will be? necessarily early 8? btdc, instead of 0? to the PMS.
Cos? the start of injection (SOI) must be advanced or advance of 8 degrees of rotation of the motor shaft.
Cos? the ECU to decide should consult his maps as a function of the
Quantity? injection request from the accelerator position and establish
the duration of injection made with the amount? injection
and the start of injection or Soi always calculated from the amount? of the injection.
Cos? a precise amount? fuel is injected for the correct amount? of time (? GR), starting exactly on time.
The control unit can? be sure of this, why? the sensors, crankshaft and camshaft shall, with the greater accuracy of the positions of the piston. These measures end up on the dashboard of the speed? the measured engine speed in revolutions per minute (rpm).
If it is only? life was really so? simple, the ecu would not need computers very powerful to determine, based on simple parameters what to do...why? if the engine is working always with a precise temperature and pressure of the air, things would be very simple.
BUT...not ? can ignore the laws of physics.And the gases and liquids behave differently at different temperatures and pressures.
Cos? the ECU must contain correction maps for the changes in temperature and pressure.
The pressure changes do not concern the majority of the people who live in close proximity? the ****llo of the sea.temperatures instead, of interest to all, why? all of the engines to start up cold and then heat up.
In a cold engine will inject more? fuel that that you should for a number of reasons.
Warm the engine,then the ecu must know that the engine is not ? more cold to stop to inject more? fuel. This pu? look like a fuel consumption of more and more? smoke from the exhaust.
for this ecu, there are correction maps.
the bike and the development of the spray of the gasoilo in the diesel engine
however, if you want to deepen the topic, you can read these lines extracted from a pdf which is also found in the network....and I have to say, as always, that what is written is not, in any way, claim to explain everything as c?? to know about. She wants only to be an introduction for those who are passionate about cars, technology and science, or just curious, want to explore further or learn something new.
In order to obtain a good combustion process of the fuel all?the inside of the combustion chamber, the characteristics of the charge injected are of primary importance.
The fast and ?intimate? mixing of the fuel with l?the air, as well as the ability? of this mixture take up a pi? volume can be between what's available, that are absolutely necessary to achieve that?goal.
The roads used by designers to achieve such effects are at least two:
- The care of the fluid dynamics with the study of the motions of the squish, tumble and swirl;
- The study of the formation of the spray and its characteristics.
The formation of very fine droplets ? of extreme importance. L?evaporation ? in fact, a process surface, as a result, the speed? with the same volume as the liquid passes to the state steam pu? be increased by increasing the liquid surface available. This allows for the rapid formation of the mixture of air and fuel and a pi? complete combustion.from this it is deduced that, for example, in the combustion chamber, the ratio between air and fuel can? vary from 0 within a microgoccia of unburned fuel to infinity in areas where the ec only to air that does not interact with the fuel....
The atomization process then ? very complex; it depends from?the interaction of the spray with l?air?the inside of the cylinder, which results in a balance of forces between the jet fluid and l?air. Obviously they have a major role in the physical and chemical characteristics of the liquid itself.
The study of such phenomena ? simple, and mathematical models exist for the pi? empirical.
You ? hypothesized that the formation of the spray is done in two phases:
- L?atomization primary;
- L?secondary atomization.
The surface of the liquid jet outgoing from?the nozzle is put in rapid oscillation. These oscillations, which are a function of the geometric characteristics of the nozzle, are amplified from?the interaction of the liquid with l?air. When their intensity? exceeds a certain limit value, which is the crushing of the jet, called primary atomization.
The drops cos? formed undergo l?action of different forces, which depend on the speed? of the drops themselves, (which in turn depends on pressure but also on the viscosity? the diesel), but also by other characteristics of the fuel (density, the surface tension). These forces determine a second fragmentation of the droplets, a phenomenon known as secondary atomization.
For what is written you can? to say that the formation of the spray, in addition to being a function of the geometric characteristics of the the nozzle (including the diameter of the holes, but not only) depends on:
- Injection pressure (increase the speed? of the drops but also l?intensity? of the aerodynamic forces);
- Internal pressure dell?the air in the cylinder;
- Properties? of the fuel;
But also by the length of?injection.
Of course, in addition to the formation of particles of small size, must be considered, as mentioned previously, the ability? of the spray to occupy the largest volume possible.
Of us? is taken into account through two parameters, the penetration of the spray and l?opening angle of the cone of spray.
- The penetration increases all?increase of the diameter of the droplet;
- Increases all?increase of the injection pressure (only up to a certain point since? high-pressure formation of very small particles that evaporate easily);
- Reduced back pressure (this effect ? maybe more? important-to-cone spray).
But let's see how these parameters work.
Pressure dependence:
In short, in the chart ? shown l?the trend of the length of penetration of the spray as a function of the supply pressure and injection time, for a nozzle-type VCO with holes from 200um in diameter.
As expected there ? a clear difference between the 60, 100 and 130MPa in the lengths of the spray , as well as in the angular coefficient of best-fit. Abnormal can? instead, appear l?the trend of the experimental data between 130 and 160MPa, where you do not notice any obvious differences.
There? ? probably due to the increased evaporation of the drops produced at 160MPa, which then can not penetrate long in the cylinder
Depending on the type of nozzles:
The test conducted on the two types of nozzles (VOC and mini-sac) , with the diameter of the holes is variable between 0.1 - 0.15 and 0.2 mm, showed a lower degree of penetration of the spray nozzles of the type VOC of equal size.
There? ? probably due to a bigger capacity? cold mist from the part of the VOC, which turns into a better rate of evaporation of the fuel.
L?the analysis could go on about the countless parameters. The shape of the spray ? in fact, dependent on the duration of?injection, the temperature of the?the air in the cylinder to equal? pressure (if not very), and by other factors such as the physical and chemical characteristics of the fuel.
It should be remembered that, although one can assume the conditions of density?, viscosity? and surface tension of the fuel, as the values in the standard conditions (1Atm and 25?C), the conditions change to temperatures and pressures that are typically present in an injector, including the density, for the liquid, and is commonly considered to be constant, given the typical incomprimibilit? of the liquids, but that 1600-2000 bar undergoes variations.
Not wanting to burden the discussion, which is supposed to be a valid approach for all, can you? ultimately to say that, when you make a change to the injection parameters (timing, advance injection, rail pressure), but also to pressure turbo, all you can? to say, except that to make a prediction about how it will come? changed the spray.
I hope not to have missed anything important in the attempt to simplify a speech very well articulated.
