"Mom, I want to buy a diesel Haval H5! Leather is against the world! "
The above two pictures can be said to sum up how many young people
"Mom, I want to buy a diesel Haval H5! Leather is against the world! "
The above two pictures can be said to sum up how many young people's "diesel dreams" have been destroyed. In the last issue of black technology, we showed you that Mazda ·HCCI transplanted the original diesel compression ignition engine to the gasoline engine. This time, let's take a look at how the diesel engine "strikes back".
When it comes to diesel engines, everyone's first reaction is often heavy trucks on the road and walking tractors in the field. Large torque, loud noise and 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-leading passenger car diesel engine technology has completely subverted our inherent concepts. 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 are high-end diesel engines rarely seen 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 mounted on diesel engines-in fact, the current diesel engines are not what we imagined.
How does a diesel engine work?
It is necessary for black technology to give you a brief introduction to 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 car, 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 (220℃), no ignition device is needed, and the mixture in the cylinder can be ignited by compression ignition, so the compression ratio of diesel engine is generally high, between 16-22.
The noise caused by high compression ratio is greater, and the most intuitive feeling is the domineering of tractor "chug chug", even the horn is saved. 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 is increased (generally 3000 rpm), the torque of the diesel engine drops obviously, and the power reaches the peak, so it can't be increased any more.
The high carbon content and complex composition of diesel fuel lead 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 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 to high torque, loud noise and vibration.
2. Diesel fuel has high carbon content → high energy density → low fuel consumption.
3. Complex composition+compression ignition mode → low fuel utilization rate and emission problems.
In this way, diesel engines seem to be only suitable for rough trucks. But why do Audi, Land Rover and other manufacturers insist on diesel engines for many years and expand the displacement to 1.4L-6.0L? Because engineers firmly believe that under the advantage of ensuring low fuel consumption and high torque, diesel engines can become more refined and cleaner, 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".
There is a doorway to fuel injection.
High voltage rail
This technology has a history of 14 years, and its great role has to be mentioned. The so-called high-pressure rail simply means that the fuel stays in a cylindrical high-pressure accumulator before being injected into each cylinder, the pressure is increased to nearly 2000 atmospheres, and the distribution is ensured to be uniform, and then it flows to the injector. * * * Common rail and injector are connected to the brain of the car-ECU, which determines the best fuel injection time and quantity.
Another contribution of * * rail technology is to separate the pressure generation 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 8 kinds of injections per working cycle. Two pre-injections make the combustion quieter, 1 main injection provides the main power, and five post-injections can reduce pollutant emissions.
Piezoelectric ejector
The high-pressure rail system makes the fuel pressure very high, so it needs an extremely accurate fuel injection device to maintain it, and the piezoelectric injector is the best match. The core structure of injector is hundreds of layers of piezoelectric crystals in piezoelectric actuator.
When a voltage is applied to the crystal, the single crystal will expand slightly and change 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 the needle valve of the fuel injector below. There is no mechanical connection between this conduction, which is the most direct. The response speed of this piezoelectric injector is four times that of the traditional injector, and it can cooperate with the common rail to control the injection more accurately. At the same time, the diameter of the oil injection hole is only 0. 1mm, which ensures good atomization of the fuel injected into the cylinder.
In other words, the combination of * * * rail technology has greatly improved the "stupid" problem of diesel engines.
Turbocharged excavation
Double turbocharging+electronic turbo assist
The exploration of supercharging technology seems endless, so does diesel engine.
Taking the new TDI model in diesel engine as an example, its 3.0TDI adopts double turbochargers in series, which makes up for the lack of power of diesel engine at high speed. When the speed is lower than 2500 rpm, the small turbocharger with variable cross-section technology completes most of the supercharging work. From about 2500 rpm, the switching valve began to open, and the small turbocharger gradually handed over the main supercharging work to the large turbocharger. When the speed is 3500-4000 rpm, the valve is fully open and only the large turbocharger is boosting.
How to make the engine have a good power output when the engine is idling and the speed is very low? 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. Under most working conditions, air will not flow through here. Only when the engine speed is low and the exhaust energy is low, the bypass valve will be closed and the air will flow through it 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 3.0TDI engine is increased from 580Nm to 750Nm, and the speed point is also advanced from 1400rpm to 1250rpm. Peak torque and platform lift are still obvious.
VTG variable turbine part
The small turbocharger mentioned above has variable turbine cross-section technology, so it is necessary to expand it here. Everyone must know the working principle of turbocharger, 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 lower energy will increase after passing through the vanes, and it will blow to the turbine at a higher speed, which will make the turbine accelerate faster. Simple understanding is like a gentle wind blowing outside. If your window is wide open, the wind coming in will be very soft. If there is only a gap in the window, you will find that the incoming wind speed is faster.
Variable cross-section turbine (VTG) is also equipped on Porsche sports cars. It is a gasoline engine technology, and now it has been extended to diesel engines. It can be seen that diesel engines have the potential for further exploration.
Exhaust emission control
SCR catalytic converter
SCR refers to the catalytic reduction of nitrogen oxides in waste gas. On the way, the red ball is nitrogen oxides, the gray ball is carbon particles, the blue ball is ammonia, and the green ball is nitrogen generated. During the operation, AdBlue solution (blue) is sprayed into the SCR catalytic converter from the storage tank. 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 and diesel particulate filter in the new 3.0TDI engine. Since AdBlue solution will solidify below 0℃, 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 used up 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, the start of SCR is avoided by software, because this device will increase the cost of car maintenance for users.
Why the Advanced Diesel Engine Encountered Embarrassment in China?
I believe everyone has a new understanding of the current diesel engine. The current technical level, complexity and environmental protection of diesel engines are no less than those of gasoline engines. At the same time, it also retains the unique advantages of diesel engines-strong low-speed power, 30-40% lower fuel consumption than gasoline engines with the same displacement, and even reaches the level of some hybrid models. In fact, at present, 60% of vehicles on European highways use diesel engines, while this figure is only 1% in China.
Diesel engines such as TDI can meet Euro 6 standards, not to mention the emission standards of China. But why is it difficult for us to see diesel cars in cities? There are two main reasons:
First-tier cities have too tight policies on diesel vehicles.
In a city like Beijing, the diesel passenger car policy is "one size fits all". No matter what skills you have, as long as you burn diesel, you won't get a license. If you insist on a foreign license, the problem of entering Beijing will follow. Complicated procedures and highly restrictive automobile regulations make many people flinch from diesel vehicles, but in the end they choose gasoline vehicles. In this regard, domestic and foreign manufacturers such as Audi, Kia and Ssangyong are also very helpless.
With technology and consumer demand, we wait for the market, but we have to wait for the policy.
Diesel problem in China
Limited purchases in big cities, but not in small cities, right? Don't worry, our oil is also a big problem. Advanced diesel engine technology requires very strict oil products, but our diesel oil often fails to meet the requirements, which is manifested in the high content of impurities and sulfides. Friends who drive must have personal experience. With the current diesel 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 have to ask petrochemical enterprises first. This is not a simple matter. To improve the quality of oil products, we must start with upgrading the (gold) level (port) equipment in the refining process. This is a multi-billion dollar investment, and it can't be done overnight.
@ 中中中中中中 believes that these two reasons are also mutually restrictive. In the government's view, no matter how good the diesel engine technology is, it is 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 heavily in upgrading 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 still very happy to see the great progress in power and emissions of diesel engines.