[YesAuto technology] In the past two days, everyone has been talking about the news that Volkswagen diesel vehicles were detected by EPA in the United States of fraudulent exhaust emissions. The engine computer equipped with cheating programs was used to avoid stringent emission tests, which led to Volkswagen owners’ Unknowingly, it adds a burden to the environment in the United States, and the public may also face huge fines. Can this computer program cause such a big wave?
● How can fake?
EPA is the English abbreviation of the U.S. Environmental Protection Agency. Only cars and motorcycles that pass this certification can be sold in the United States. The emission test conducted by the EPA is essentially similar to the exhaust gas test we conduct in the annual inspection. Of course, the test standards and details of the test will also be different.
In this way, the emission test from EPA is not so mysterious. In my early work experience, there were many opportunities to see crooked ways in order to pass the exhaust gas test, such as removing the air filter element (increase the air intake), and disconnecting the crankcase ventilation pipe (not letting the oil vapor Participation in combustion) These tricks are relatively elementary, and the earlier common distributor type ignition can reduce the engine power by slowing the ignition time, and then restore the various parts after passing the test. This is a relatively primitive and unofficial test-taking measure.
After talking for a long time, it seems that it has nothing to do with the public fraud. In fact, it is not. At the technical level, many principles are the same. Of course, the public cannot make artificial adjustments before and after the EPA test. If the facts of the fraud are conclusive, then how did the public use the so-called illegally implanted emission control software to conceal the truth?
Different from human adjustment, the first thing the control program has to do is to recognize the test like a human, to be precise, to recognize the EPA test. In the exhaust emission test, the vehicle is placed on the test bench, and the tester keeps the engine running within the speed range required by the test. In some cases, quick refueling is used to make the engine reach a specific speed in a short time. In terms of conditions, there are obvious differences from the working conditions required for daily driving. It is feasible to identify the test conditions through the understanding of the EPA test and the targeted data calibration. On the other hand, other peripheral data can also be used as the basis for judging the start of the program. Essentially, this is the same as when you step on the accelerator and the gearbox will downshift. You did not make a downshift or even have the awareness of downshifting, but in order to cater to your acceleration needs, the manufacturer passes data calibration The speed is increased by downshifting.
● Bosch is an accomplice?
Bosch occupies a large share of the global market in terms of diesel common rail and control technology. This time, the fuel control system provided by Bosch is used in the cheating models exposed by Volkswagen, including the ECU that carries the cheating program. Is this Does it mean that Bosch participated in the calibration of the cheating program?
In the internal development and verification work of some domestic manufacturers that we have previously participated in, suppliers like Bosch will indeed participate in the data calibration process and help the OEM to improve the construction of the engine control program. For international manufacturers such as Mercedes-Benz, BMW, Audi or Volkswagen, the calibration technology is their foothold in this industry. Based on their own huge data accumulation, each manufacturer conducts corresponding calibration work for different products and markets. And vendors like Bosch will only provide hardware and underlying data support. From the perspective of international practice, if the cheating procedure is conclusive, it should be a unilateral act of the public. This is like the Edison Chen’s Yanzhao incident. You can’t just arrest the computer manufacturer just because he saved the video on the computer. It’s a truth.
● Is there really nothing to do in the face of diesel engine emissions?
In our cognition, diesel engines are always associated with black smoke, loud noises, difficulty in cold starting, and low power. However, in Western countries, diesel engines are considered to be the cleanest before the arrival of the new energy era. This is a kind of internal combustion engine technology, but does Volkswagen’s recent presentation make it time for us to draw a question mark on the application of diesel engines in the passenger car field? Is it true that the technology for improving the emission quality of diesel engines is really poor?
● How to “perfect” the drawbacks of diesel engines in the traditional perception?
The application of in-cylinder high-pressure direct injection, variable-section turbocharger, exhaust gas circulation and after-treatment technology has curbed the defects of diesel engine to a certain extent, so that its high-efficiency and high-torque characteristics are retained. Of course, based on long stroke Due to the cylinder structure, the speed of the diesel engine is lower than that of the gasoline engine. Therefore, the power is a short board in terms of power data. However, combined with the use of modern gearbox technology, the engine speed can also be obtained in daily driving and high-speed cruising conditions. control.
● What is the difference between a diesel engine and a gasoline engine?
First of all, it is certain that in the field of exhaust emission control technology, diesel engines have always been ahead of gasoline engines, which is inseparable from the characteristics of the oil and the working principle of the engine.
◆ Working principle of diesel engine
The fuel ignition method is the biggest difference between the two. Gasoline engines use spark plugs to ignite the fuel injected into the cylinders, while diesel engines use the rising cylinder pressure to generate heat to ignite the fuel based on different pilot fuels. the way. The two types of engines also have obvious differences in cylinder parameters. The compression ratio of gasoline engines is much lower than that of diesel engines. A higher compression ratio can release more energy and increase efficiency is also a recognized law. Therefore, in the research and development of gasoline engines, engineers also began to implant the concept of high compression ratio.
In fact, in today’s gasoline engines, you can see many technologies borrowed from diesel engines. We are most familiar with in-cylinder direct injection and its high-pressure common rail technology. With the improvement of emission regulations, there will be More technologies that have been popularized on diesel engines are grafted onto gasoline engines, such as EGR.
● EGR exhaust gas recirculation technology
EGR is a very common device in diesel engines. It reduces the nitrogen oxides in the exhaust gas by re-directing the exhaust gas discharged from the exhaust valve to the intake side for secondary combustion. Since the exhaust gas has a higher temperature, direct introduction of it into the combustion chamber will cause the combustion environment to continue to deteriorate, so it must pass through a cooling device before completing the cycle.
Now, on some gasoline engines, such as the Honda Earth Dream engine mounted on the Fit and Accord, the EGR structure can also be seen, but in fact, EGR has not been applied to gasoline engines in the past two years. As early as the V6 engine equipped on Audi's fifth-generation A6 model, this technology was tried. In the later technical development, engineers used the blessing of variable timing technology, the advancement of catalytic technology, and the improvement of lubrication and cooling technology. Optimization, etc., can meet the emission requirements at the time, so the complicated EGR system is omitted. Of course, for gasoline engines at this stage, EGR is a way to improve emission quality.
For passenger cars at this stage, most of the exhaust gas control part will use the EGR system at the front end to carry out the secondary exhaust gas circulation, and then use the catalytic converter to convert the nitrogen oxides, and install the particulate filter at the rear end to reduce dust. Emissions. Nevertheless, in the face of increasingly stringent regulatory requirements, such a technical configuration may also usher in a bottleneck, and the already mature SCR is the best exhaust gas treatment solution for diesel engines.
● SCR will save the fate of diesel engines in passenger cars
For the EPA, 2010 is the end of an era. In fact, the previous era only stayed between 2007 and 2010. The era has changed due to the improvement of testing standards. The previous standards rely on the above-mentioned EGR and catalytic The technical optimization of the engine and the engine itself may be barely achieved. Indeed, judging from industry reports, even if the EPA test under the old standard is passed or not, there is a strong uncertainty. In other words, if you want to pass the EPA now, the previous set of equipment will no longer work. But as far as I know, it seems that no manufacturer has used the new technology in front of us (the implication is that with the EPA's larger-scale detection of this matter, more companies that cheat may be found), why No need to? What exactly is SCR?
SCR is called the selective catalytic reduction system. By injecting a urea water solvent into a device containing precious metal and non-precious metal catalysts, through more complex physical and chemical reactions, the nitrogen oxides in the exhaust gas are processed to achieve the purpose of reducing emissions. . For the treatment of nitrogen oxides, SCR has a very significant effect. It has been confirmed by the industry that under different working conditions, SCR can reduce nitrogen oxide emissions by 65% to 99%.
At present, SCR technology is the more mainstream technology route, and it has been widely used in commercial vehicles equipped with diesel engines. Then, why has this technology been delayed to be installed on passenger car bodies?
In my opinion, there are two reasons. One is the cost reason that everyone recognizes. The complicated technical structure requires the OEM to reconsider the installation layout and closed-loop control data calibration. On the other hand, it is the convenience of use and the daily use. In a car, urea is continuously consumed as the vehicle moves. Generally, about 5L of urea aqueous solution is consumed to burn 100L of fuel.
Such consumption means that a space for a urea solution storage tank needs to be reserved in passenger cars with limited layout space. It can be imagined that the volume of a general glass water storage tank is less than 3 liters, and it must be in the engine compartment. Occupy a large space, and a container with a volume of at least 5 liters (this volume means that the urea solvent used for the catalytic reaction will be replenished every two fuels). We want to pay more and more attention to maximizing the interior space of the car It’s really difficult to find a place in your passenger car. Not only that, this step is too troublesome for the owner of a passenger car.
In summary, due to cost, design and development, and convenience of subsequent use, it may become the root cause hindering passenger car diesel engines from passing the EPA test for a period of time, or it will also prompt updated emission control. Technology is born.
From a purely technical point of view, this program for exhaust emission testing belongs to the scope of engine adaptation to working conditions, just like some manufacturers have set a dynamometer mode for their own models, usually you don’t use the data under the dynamometer state at all. . Of course, things must not be that simple. If we jump out of technical discussions, we still cannot put the two things together. Whether it is fuel consumption or exhaust emission testing, it should take into account more actual operating conditions as much as possible. The single operating condition test is not rigorous, and setting a test condition in the ECU for testing is even more contrary to the manufacturer’s expectations of the society. Responsibility. We will continue to pay attention to the issue of emission test education. In any case, I hope to see technologies that are more suitable for use in passenger car diesel engines to improve exhaust gas quality are put into use sooner. (Photo / Li Boxu, the home of the car)