“Mom, I want to buy a diesel Haval H5! Pichina is the best in the world!”

The above two pictures can be said to sum up a lot. How young people's "diesel car dream" was ruined. In the last issue of Black Technology, we showed you how Mazda HCCI transplanted the original diesel compression ignition to a gasoline engine. This time we will take a look at how the diesel engine "counterattacks".

When people think of diesel engines, their first thoughts are often of heavy trucks on the road and walking tractors in the fields. Rough torque, huge noise and billowing black smoke have become Chinese people's consistent impression of diesel engines. Little did they know that time passed by, and engineers’ research on diesel engines, just like gasoline engines, never stopped. At present, the world's leading passenger car diesel engine technology has completely subverted our inherent ideas about it. In this regard, passenger car diesel engines launched domestically include Oyide, Huatai and other brands, while foreign companies that are doing better include Audi TDI, Land Rover's TD series, etc.

Why can "extensive" diesel engines be used in luxury models? Why do we rarely see high-end diesel models in our country? Today's @车黑科技, we have prepared a lot of useful information to share with you all the various awesome technologies currently equipped on diesel engines - in fact, today's diesel engines are no longer what we think they are.

How does a diesel engine work?

Black Technology needs to briefly introduce to you the working principle of the diesel engine. At present, the vast majority of passenger cars use four-stroke diesel engines, while two-stroke diesel engines are more commonly used in large trucks and tractors. If you understand the working process of your car's gasoline engine, then the four-stroke diesel engine is not difficult to understand.

The working principle of a four-stroke diesel engine is similar to that of a gasoline engine. Each working cycle consists of four strokes: suction, compression, power, and exhaust. The difference is that due to the low ignition point of diesel (220°C), there is no need for an ignition device. The fuel mixture in the cylinder can be ignited using compression ignition. Therefore, the compression ratio of diesel engines is generally higher, between 16-22 between.

High compression ratio brings greater noise. The most intuitive feeling is the domineering "chugging" of the tractor, even the horn is omitted. On the other hand, the high compression ratio and the characteristics of diesel engines also make the torque of diesel engines at low speeds significantly higher than that of gasoline engines. This is the root of what we usually call "powerful diesel engines". However, after the speed increases (usually 3000rpm), the diesel engine torque drops significantly and the power reaches its peak and cannot be increased.

Diesel has a high carbon atom content and complex composition, which results in low fuel utilization rate of traditional diesel engines. Due to incomplete combustion, the contents of nitrogen oxides, sulfur-containing compounds, and carbon-containing particulate matter in the emissions are also very high. This is the reason for "black smoke and strong smell".

To sum up, traditional diesel engines have the following characteristics:

1. Compression ignition method → ??high compression ratio → low rotation and high torque, large noise and vibration

2 , Diesel has high carbon content → high energy density → low fuel consumption

3. Complex composition and compression ignition method → ??low fuel utilization and emission problems

From this point of view, it seems that diesel engines are only suitable for What a rough truck. But why have Audi, Land Rover and other manufacturers insisted on diesel engines for many years and expanded the displacement to 1.4L-6.0L? Because engineers firmly believe that diesel engines can become more refined and cleaner while 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 to transform them from "silly, big, black and rough" to "Xiaojiabiyu".

There is a way to fuel injection

·High-pressure injection rail

This technology has been around for 14 years now, and its role must be mentioned . The so-called high-pressure fuel rail simply means that before the fuel is injected into each cylinder, it first "stays" in a cylindrical high-pressure accumulator. The pressure is increased to nearly 2,000 atmospheres and is ensured to be evenly distributed. Then flows to the injector.

Both the rail and the injector are connected to the brain of the car - the ECU, which determines the optimal injection time and amount of fuel.

Another contribution of ***rail technology is that it separates the generation of pressure from the injection of fuel. Engineers can freely configure all injections, bringing a great degree of freedom to development and design. For example, Audi's TDI diesel engine can classify 8 types of injections in each working cycle. 2 pre-injections make combustion quieter, 1 main injection provides main power, and 5 post-injections can reduce pollutant emissions.

·Piezoelectric fuel injector

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

When a voltage is applied to the crystal, the single crystal expands slightly, rapidly changing its structure in a thousandth of a second. Hundreds of piezoelectric wafers are stacked in the injector, producing obvious quantitative changes that push open the injector needle valve below. This transmission has no mechanical connection in the middle and is the most direct. The response speed of this kind of piezoelectric injector is 4 times that of traditional injectors, and it can more accurately cooperate with the central rail to control fuel injection. At the same time, the diameter of the fuel injection hole is only 0.1mm to ensure that the fuel injected into the cylinder is well atomized.

In other words, the combination of rail technology has greatly improved the "stupid" problem of diesel engines.

The exploration of turbocharging

·Twin-turbo electronic turbo assist

The exploration of supercharging technology seems to be endless, and the same is true for diesel engines .

Take the new TDI model of diesel engines as an example. Its 3.0TDI uses series twin turbochargers to make up for the lack of power of the diesel engine at high speeds. Below 2500rpm, a small turbocharger with variable cross-section technology does most of the boosting work. From about 2500rpm, the switching valve begins to open, and the small turbocharger gradually transfers the main boosting work to the large turbocharger. At 3500-4000rpm, the valve is fully open and only the large turbocharger is boosting.

How to make the engine have good power output during the idling starting stage and at a very low speed? Audi has come up with such an innovative idea - electronic turbine. This device is equivalent to a compressor, driven by an electric motor, and is located downstream of the intercooler. Under most working conditions, air will not flow through here. Only at lower engine speeds and when the energy of the exhaust gas is low, the bypass valve will be closed and the air will flow through here and be pressurized. Because it is driven by electricity, engineers specially provided a 48V circuit for this electronic turbine, combined with a braking energy recovery function.

After installing the electronic turbine, the peak torque of this 3.0TDI engine has been increased from 580Nm to 750Nm, and the speed point has also been advanced from 1400rpm to 1250rpm. The improvement of the torque peak and platform is still obvious.

·VTG variable turbine section

It is mentioned above that the small turbocharger has variable turbine section technology, and it is necessary to expand on it here. Everyone must understand the working principle of a turbocharger, but what does variable cross-section mean? It turns out that there is a circle of guide vanes around the turbine, and the exhaust gas blows to the turbine after passing through the guide vanes. When the driver deeply steps on the accelerator, the guide vanes will rotate under the action of mechanical pressure, and the angle between the vanes will become smaller. In this way, the flow rate of exhaust gas with low energy will increase after passing through the vanes, and flow at a higher speed. Blow towards the turbine to activate it faster. To understand it simply, it's like a gentle wind blowing outside. If your window is wide open, the wind blowing in will be very gentle; if there is only a crack in the window, you will find that the wind speed incoming becomes faster.

Variable turbine geometry (VTG) is also installed on Porsche sports cars. It is a gasoline engine technology. Now it has been extended to diesel engines. It can be seen that diesel engines have further potential to be explored.

Emission Control

·SCR Catalytic Converter

SCR refers to the catalytic reduction of nitrogen oxides in the exhaust gas. The red balls on the way are NOx, the gray are carbon particles, the blue are ammonia, and the green are the generated nitrogen. During operation, AdBlue solution (blue) is injected from the storage tank into the SCR catalytic converter. This water-soluble additive breaks down in hot exhaust gases to produce ammonia, which converts nitrogen oxides into harmless nitrogen and water. Audi combines an SCR catalytic converter with a diesel particulate filter in the new 3.0TDI engine. Since the AdBlue solution will solidify below 0°C, Audi has equipped the catalytic converter with an electric heating function.

One more thing, we usually call the additive AdBlue urea. The name is not pleasant, but it does contribute a lot to the suppression of nitrogen oxide emissions. In addition, AdBlue is a consumable product, so don’t wait until it is exhausted before adding more in daily use. Last year, Volkswagen failed to cheat on emissions cheating in the United States and suffered the biggest loss in the company's history. In fact, it was using software to avoid the activation of SCR, because this device will increase the user's car maintenance costs.

Why are advanced diesel engines in embarrassment 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 engines - strong power at low speeds and fuel consumption 30-40% lower than gasoline engines of the same displacement, even reaching the level of some hybrid models. In fact, currently 60% of the models on European roads use diesel engines, but this number is only 1 in our country.

Diesel engines like TDI can meet Euro 6 standards, and China’s emission standards are naturally not a problem. But why is it so difficult for us to see diesel cars in cities? The main reasons are as follows:

·First-tier cities have too tight policies on diesel vehicles

In cities like Beijing, the diesel passenger vehicle policy is “one size fits all”, regardless of your technology , as long as you burn diesel, you cannot get a license. If you insist on obtaining a foreign license, the problem of entering Beijing will arise. The complicated procedures and highly restrictive car regulations have made many people shy away from diesel cars, and they have no choice but to choose gasoline cars. In this regard, domestic and foreign manufacturers such as Audi, Kia, and Ssangyong are also helpless.

With technology and consumer demand, we have waited for the market, but we still have to wait for policies.

·my country’s diesel oil problem

There are purchase restrictions in big cities, but not in small cities? Don’t worry, our oil is also a big problem. Advanced diesel engine technology has relatively strict requirements for oil products, but our diesel often fails to meet the requirements, which is manifested in the high content of impurities and sulfides. Friends who drive must have experienced this firsthand. The current diesel oil products in our country can only satisfy the extensive, backward and inefficient diesel engines on the highway.

Improving oil quality is the most direct way, but you must ask petrochemical companies first. This is not something to simply talk about. To improve oil quality, we must start with the refining process and upgrade (jin) level (kou) equipment. This is an investment that can cost billions to tens of billions and cannot be completed overnight.

@车黑科技 believes that these two reasons are also constraining each other. From the government's point of view, if the oil quality is not improved, no matter how good the diesel engine technology is, it will be difficult to meet the standards, so I will not lift the ban; and from the petrochemical company's point of view, if the government does not relax the ban on diesel passenger cars, why should I invest huge sums of money to improve the oil quality?

I hope that one day, not only the price but also the quality of my country's "three barrels of oil" will be in line with international standards. Back to technology, although the current domestic status quo cannot fully meet the working conditions of advanced diesel engines, it is a happy thing to see the huge progress of diesel engines in terms of power and emissions.