Not long ago, he took part in Bosch's diesel SUV test drive meeting held in Kunming, and heard the phrase “Japan's diesel vehicles are developing rapidly†during the chat and found it very interesting. In the author's impression, Japan is only playing a gasoline engine and hybrid power, and deepening into fuel cell vehicles. Diesel vehicles are only prevalent in Europe and have nothing to do with Japan.
However, turning over Japan's new energy vehicle program found that clean diesel vehicles are among them. In recent years, the proportion of diesel engine loading in the Japanese market has also been quietly increasing. In 2013, the sales volume of diesel vehicles in Japan reached 75,000 vehicles. In 2011, it was only 8638 vehicles, which increased by about 9 times in two years. Although it is not occupied by half of Europe in terms of quantity and proportion, its growth rate is really impressive.
Even more worthy of our attention is that diesel engines are gradually advancing to the compact car market in Japan on a miniaturized route. This is a completely different route from the development of European diesel power. This change in details is unlikely to be soon to the car. The market has far-reaching influence.
Technological progress highlights the advantages of diesel engines
The most intuitive impression left by traditional diesel power is the thick black smoke, violent vibrations, and extremely poor high-speed performance. Of course, these traditional cognitions are based on conventional heavy duty diesel engines with diesel. In fact, the use of clean diesel oil in the European market and the popularity of high pressure common rail technology have greatly improved the black smoke and noise of traditional diesel engines. The advantages of diesel engines are also more glorious because of the application of new technologies.
The advantages of diesel engines are mainly concentrated on two aspects: high-efficiency and energy saving, and low carbon oxide emissions. Because of the difference in combustion characteristics, the thermal efficiency of diesel engines is about 30% higher than that of gasoline engines, and the average fuel consumption is also 30% lower on average. Since the combustion of the diesel engine is in an oxygen-rich state, the emission concentrations of CO and HC compounds are relatively low, and the concentrations of particulate matter and NO compounds are high. In recent years, the use of diesel post-processing technologies such as urea and diesel particulate filtration has resulted in a significant reduction in the emissions of particulate matter and NO compounds.
It is precisely for this reason that this feature of diesel vehicles has been paid attention to and has been widely used in the European market where the greenhouse effect is becoming more and more important. Then, when the Japanese automobile market has made great strides in small-displacement gasoline engine technology and hybrid technology, why is it interested in diesel engines? The author believes that there are at least the following two aspects:
The first is Japan's JC08 test regulations. As we all know, the JC08 in Japan is one of the most rigorous in the world's mainstream fuel consumption testing procedures. The reason why it is harsh is mainly because it pays more attention to the assessment of cold-start emissions, acceleration and deceleration conditions, etc. The fuel consumption performance under the JC08 model is much higher than that under other test procedures. According to experience, the fuel consumption of the same model under the JC08 test procedure is 1-2L higher than that of the European NEDC code.
At the same time, Japan’s new vehicle fuel consumption management measures will be implemented in 2020. According to the new management approach, the weighted average fuel consumption of all vehicle models of each automobile company must reach 20.3Km/L under the JC08 test cycle. 4.9L/100Km. On one side is a harsh test that is close to everyday life, and on the other is the same harsh emission standard. It is clear that Japanese auto companies are not less pressured by restrictions on fuel consumption than Chinese companies.
The second is the cost factor. Although Japanese auto makers have made great strides in hybrid technology, the hybrid power is necessarily higher than traditional internal combustion engines. In the Japanese market, small cars and even K-Cars occupy a larger market share. The price and profit of these models are very low, making it difficult to popularize hybrid systems to further reduce fuel consumption. Under such circumstances, the Japanese auto companies have made the diesel engine miniaturization the direction of another “new energy†and have become a success.
How to move away from the stumbling block in the miniaturization of diesel engines. What are the technical difficulties facing the miniaturization of diesel engines?
The first is the size. Compared to gasoline engines of the same displacement, diesel engines are larger and taller in terms of overall size and weight because of the greater cylinder pressure experienced by the diesel engine and the longer piston stroke. On the one hand to meet the requirements of mechanical performance, on the other hand to meet the compactness requirements of small cars, so the design of the diesel engine block will need to spend more energy to balance the needs of these two areas.
This is followed by the setting of the technical parameters of the cylinder block of a small-displacement diesel engine. Diesel compression ignition determines that it must have a larger compression ratio to obtain greater in-cylinder pressure. However, the increase in compression ratio inevitably brings problems such as vibration and noise, and the load on the piston and the crankshaft must also increase accordingly. If the experience of compression ratio design of conventional diesel engines is followed, then small-displacement diesel engines will inevitably have shortcomings in these areas. Therefore, to make the diesel diesel engine small, the compression ratio must be reduced.
However, the problem came again. Once the compression ratio is reduced, it will lead to incomplete diesel combustion or even a lack of fire. In this process must involve the application of lean combustion technology, generally speaking, the compression ratio of passenger car diesel engine is between 16-18, but if you want to do a small displacement of a few liters, the compression ratio should be lower At present, the minimum compression ratio of Japan's small-displacement diesel engine has already reached 14.8.
So how to ensure the impact of lower compression ratio on the combustion performance of small-displacement diesel engines, or how to achieve a more lean burning? Japanese companies have given such solutions.
First, atomized diesel fuel is sent to the cylinder in advance. Conventional diesel engines supply atomized diesel fuel into the cylinder at the end of the compression stroke to achieve compression ignition. In the case where the compression ratio is reduced, the pressure in the cylinder at the end of the compression stroke is small and the combustion of the combustible gas is insufficient. In order to solve the problem, by supplying a small amount of atomized diesel fuel into the cylinder before the end of the compression stroke, the air flow is guided by the organized air flow in the cylinder, and the concentration of the air-fuel mixture in the local part of the cylinder is relatively high to achieve a uniform air-fuel mixture. Stratified combustion greatly improves the in-cylinder combustion characteristics.
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Diesel high pressure common rail components
The advantage of this stratified combustion for diesel engines is that because of the prolonged mixing time of diesel fuel spray and air, the mixing of fuel and air is more uniform, which avoids the high-temperature flame zone and high-temperature over-concentration zone in the early stage of traditional diesel engine ignition. The local flame temperature is made lower than the temperature that favors the formation of nitrogen oxides, reducing the nitrogen oxide emissions. On the other hand, since the diesel fuel mixture is more uniform within the cylinder, the smoke generated due to lack of oxygen can also be avoided. Therefore, even if no emission reduction methods such as urea are used, diesel engines with low compression ratios can also achieve superior emission performance.
The problem still exists in that, due to the reduction of the compression ratio of small-displacement diesel engines, the contribution of piston negative pressure to the intake pressure is also small, and the problem of insufficient intake pressure is very likely to occur. Japan solved this problem with variable cross-section turbocharging technology.
Compression ratio to reduce the oil pressure will inevitably increase, if not in recent years, the popularity of common-rail diesel injection technology, the traditional piston-type fuel pump in any case can not guarantee the oil supply pressure of small-displacement diesel engines. In other words, the popularity of common-rail technology has paved the way for the miniaturization of diesel engines in recent years. In fact, this series of changes can be attributed to the integration of diesel engine and gasoline engine technology in recent years. The dieselization of gasoline engines and the petrolization of diesel engines will surely become the mainstream of the development of internal combustion engines in the future.
With the miniaturization of diesel engines, higher requirements have also been placed on the precision of fuel supply system components such as injectors. If the oil product does not pass, the entire fuel supply system of the small-displacement diesel engine will become very poor. Therefore, in front of the diesel engine, the word "clean" must be added.
Obviously, with the advancement of engine technology and the popularity of clean diesel, the development of small-displacement diesel engines has become possible. When a small car meets a small-displacement diesel engine, the combination of the two must be an advantageous combination. When global automotive companies are facing stringent emissions and fuel consumption regulations, entry-level small vehicles carry small Displacement diesel power is undoubtedly the best way to balance costs and regulations. While Japan is vigorously promoting hybrid power and fuel cell power, it is also focusing on the development of small-scale diesel power. This is very worthy of our attention.