"Mom, I want to buy a diesel Haval H5! Pishi is resistant to the world! "

The above two pictures can be said to sum up how many young people's "diesel dream" was ruined. In the last issue of black technology, we showed you that Mazda HCCI transplanted the original diesel compression ignition to the gasoline engine. This time, let's take a look at how the diesel engine "counterattacked".

When it comes to diesel engines, people's first reaction is often heavy trucks on the road and walking tractors in the fields. Rough torque, loud noise and billowing black smoke have become the consistent impression of Chinese people on diesel engines. Little did they know that time flies, and engineers never stopped studying diesel engines like gasoline engines. At present, the world's leading passenger car diesel engine technology has completely subverted our inherent concept. In this regard, domestic passenger car diesel engines have brands such as Ouyide and Huatai, and foreign brands have done better, such as Audi TDI and Land Rover TD series.

why can "extensive" diesel engines be used in luxury models? Why do we seldom see high-end diesel engines in China? Today's @ Auto Black Technology, we have prepared a lot of dry goods to share with you all kinds of great technologies currently carried on the diesel engine-in fact, the current diesel engine is no longer what we think.

how does a diesel engine work?

it is necessary for black technology to briefly introduce the working principle of diesel engines. At present, most passenger cars use four-stroke diesel engines, while two-stroke diesel engines are more used in large trucks and tractors. If you know the working process of the gasoline engine of your own car, then it is not difficult to understand the four-stroke diesel engine.

The working principle of a four-stroke diesel engine is similar to that of a gasoline engine, and each working cycle consists of four strokes: intake, compression, work and exhaust. The difference is that because the ignition point of diesel oil is low (221℃), there is no need for an ignition device, and the fuel mixture in the cylinder can be ignited by compression ignition, so the compression ratio of diesel engines is generally high, ranging from 16 to 22.

the high compression ratio brings more noise, and the most intuitive feeling is the domineering of the tractor, which saves the horn. On the other hand, the high compression ratio and the characteristics of diesel itself also make the torque of diesel engine obviously higher than that of gasoline engine at low speed, which is the root of what we usually call "strong diesel engine". However, after the speed increases (generally 3111rpm), the torque of diesel engine decreases obviously, and the power reaches the peak, so it can't be increased any more.

The content of carbon atoms in diesel oil is high and its composition is complex, which leads to the low fuel utilization rate of traditional diesel engines. Due to incomplete combustion, the contents of nitrogen oxides, sulfur-containing compounds and carbon-containing particles in the emissions are also very high, which is precisely the reason for "black smoke and strong smell".

To sum up, the traditional diesel engine has the following characteristics:

1, compression ignition mode → high compression ratio → low torque, large noise and vibration

2, high carbon content of diesel oil → high energy density → low fuel consumption

3, complex composition+compression ignition mode → low fuel utilization rate and emission problems

. But why do Audi, Land Rover and other manufacturers insist on diesel engines for many years, and expand the displacement to 1.4L-6.1L? Because engineers firmly believe that diesel engines can become more refined and cleaner under the advantage of ensuring low fuel consumption and high torque, and they have done it. Then let's take a look at what technologies are used in advanced diesel engines, from "stupid big black thick" to "small jasper".

fuel injection has a doorway

high pressure * * * rail

this technology has a history of 14 years now, and its great role has to be mentioned. The so-called high-pressure rail simply means that before the fuel is injected into each cylinder, it "stays" in a cylindrical high-pressure accumulator, the pressure is increased to nearly 2111 atmospheres, and the distribution is ensured to be uniform, and then it flows to the injector. * * * rail and injector are connected to the brain of the car-ECU, which determines the best injection time and quantity.

another contribution of * * * rail technology is that it separates the generation of pressure from fuel injection, and engineers can freely configure all injections, which brings great freedom for development and design. For example, Audi's TDI diesel engine can classify eight kinds of injections in each working cycle. Two pre-injections make the combustion quieter, zero main injection provides the main power, and five post-injections can reduce pollutant emissions.

Piezoelectric fuel injector

The high-pressure rail system makes the fuel pressure very high, so it needs an extremely accurate fuel injection device to Hold it, and the piezoelectric fuel injector is the best match. The core structure of the injector is hundreds of layers of piezoelectric crystals in the piezoelectric actuator.

when a voltage is applied to the crystal, the single crystal expands slightly and changes its structure rapidly within one thousandth of a second. Hundreds of piezoelectric wafers are stacked in the fuel injector, which produces obvious quantitative change and pushes open the needle valve of the fuel injector below. This conduction has no mechanical connection in the middle and is the most direct. The response speed of this piezoelectric fuel injector is four times that of the traditional fuel injector, and it can cooperate with the rail more accurately to control fuel injection. At the same time, the diameter of the fuel injection hole is only 1.1mm, so as to ensure that the fuel injected into the cylinder is atomized well.

in other words, the combination of * * * rail technology has greatly improved the problem of "stupidity" of diesel engines.

the exploration of turbocharging

double turbocharging+electronic turbocharging

it seems that there is no end to the exploration of turbocharging technology, and so is the diesel engine.

Take the new TDI model in diesel engine as an example, its 3.1TDI uses double turbochargers in series to make up for the power shortage of diesel engine at high speed. When the speed is lower than 2511rpm, the small turbocharger with variable cross-section technology completes most of the supercharging work. From about 2511rpm, the change-over valve began to open, and the small turbocharger gradually handed over the main supercharging work to the large turbocharger. When the rotating speed is 3511-4111rpm, the valve is fully opened, and only the large turbocharger is boosting.

how to make the engine have a good power output even at a low speed at the idle start stage? Audi came up with such an innovative idea-electronic turbine. The device is equivalent to a compressor, driven by a motor and located downstream of the intercooler. In most working conditions, air will not flow through here. Only at a low engine speed and low exhaust energy, the bypass valve will be closed and air will flow through here for pressurization. Because it is driven by electricity, engineers specially provided a 48V circuit for this electronic turbine, combined with the braking energy recovery function.

after installing the electronic turbine, the peak torque of this 3.1TDI engine is increased from 581Nm to 751Nm, and the speed point is also advanced from 1411rpm to 1251rpm, so the peak torque and platform are obviously improved.

vtg variable turbine section

The small turbocharger mentioned above has variable turbine section technology, so it is necessary to expand it here. The working principle of turbocharger must be known to everyone, so what does variable cross section mean? It turns out that there is a circle of guide vanes around the turbine, and the exhaust gas will blow to the turbine after passing through the guide vanes. When the driver steps on the accelerator deeply, the guide vanes will rotate under the action of mechanical pressure, and the included angle between the vanes will become smaller, so that the flow velocity of the exhaust gas with low energy will increase after passing through the vanes, and it will blow to the turbine at a higher speed, so that the turbine will be accelerated more quickly. Simply understood, it is like a soft wind blowing outside. If your window is wide open, the wind blowing in will be very soft. If there is only a gap in the window, you will find that the incoming wind speed becomes faster.

variable cross-section turbine (VTG) is also installed on Porsche's sports car, which is a gasoline engine technology. Now it has been extended to diesel engines, which shows that diesel engines have the potential for further exploration.

emission control

SCR catalytic converter

SCR refers to the catalytic reduction of nitrogen oxides in exhaust gas. On the way, the red ball is NOx, the gray ball is carbon particles, the blue ball is ammonia, and the green ball is generated nitrogen. During operation, AdBlue solution (blue) is sprayed from the storage tank into the SCR catalytic converter. This water-soluble additive decomposes in hot waste gas to generate ammonia gas, which converts nitrogen oxides into harmless nitrogen and water. Audi combines SCR catalytic converter with diesel particulate filter in the new 3.1TDI engine. Since AdBlue solution will solidify below 1℃, Audi has equipped the catalytic converter with electric heating function.

By the way, AdBlue is an additive, which we usually call urea. The name is not nice, but it does contribute a lot to the emission suppression of nitrogen oxides. In addition, AdBlue is a consumable, so don't wait until it is exhausted before adding it to your daily car. Last year, Volkswagen cheated in the United States and suffered the biggest loss in the company's history. In fact, it was evading the start of SCR through software, because this device would increase the cost of car maintenance for users.

why advanced diesel engines are embarrassed in China

I believe everyone has a new understanding of the current diesel engines. The current technical level, complexity and environmental friendliness of diesel engines are no less than those of gasoline engines. At the same time, it also retains the unique advantages of diesel engine-strong power at low speed, 31-41% lower fuel consumption than gasoline engines with the same displacement, and even reaches the level of some hybrid vehicles. In fact, at present, 61% of the vehicles on European highways use diesel engines, but this figure is only 1% in China.

diesel engines such as TDI can meet the Euro 6 standard, so the emission standard of China is not to mention. But why is it difficult for us to see diesel cars in cities? The main reasons are as follows:

The policies of first-tier cities on diesel vehicles are too tight

In cities like Beijing, the policies on diesel passenger cars are "one size fits all". No matter what technology you have, as long as you burn diesel, you can't get a license. If you insist on a foreign license, the problem of entering Beijing will follow. Complicated procedures and highly restrictive car regulations have discouraged many people from diesel vehicles, but they finally chose gasoline vehicles. In this regard, domestic and foreign manufacturers such as Audi, Kia and Ssangyong are also helpless.

with technology and consumer demand, we wait for the market, but we have to wait for the policy.

diesel oil problems in China

big cities have purchase restrictions, but small cities don't, do they? Don't worry, our oil is also a big problem. Advanced diesel engine technology has strict requirements for oil products, but our diesel oil often fails to meet the requirements, which is manifested in the high content of impurities and sulfides, which friends who drive must have personal experience. With the current diesel oil products in China, it can only meet the extensive, backward and inefficient diesel engines on the road.

improving oil quality is the most direct way, but you should ask petrochemical enterprises first. This is not a simple matter. To improve oil products, we must start with upgrading (jin) grade (kou) equipment in the oil refining process. This is a multi-billion-dollar investment, which cannot be completed overnight.

@ Auto Black Technology believes that these two reasons are also mutually contained. In the government's view, no matter how good the diesel engine technology is, it will be difficult to meet the standard, so I will not lift the ban; In the view of petrochemical enterprises, if the government does not relax the ban on diesel passenger cars, why should I invest huge sums of money to upgrade oil products?

I hope that one day, China's "three barrels of oil" will not only be in line with international standards in terms of price and quality. Back to technology, although the current domestic situation can not fully meet the working conditions of advanced diesel engines, it is a pleasure to see the great progress of diesel engines in terms of power and emissions.