Two-stroke diesel engines: the principle of operation, the device, pluses and minuses

A modern diesel engine is an efficient device with high efficiency. If before the diesel were put on agricultural machinery (tractors, combines, etc.), then they are currently equipped with ordinary city cars. Of course, someone has a diesel associated with black smoke from the exhaust pipe. For a while it was so, but now the exhaust system has been modernized, and there is practically no such unpleasant consequence. Let's look at two-stroke diesel engines and their features.

Some general information

A key feature of the diesel engine is its increased efficiency. This is due largely to fuel, which is 15% more efficient. If you look at the fuel at the molecular level, then here we see a long chain of carbon. Due to this, the output of the diesel fuel efficiency is somewhat higher than that of gasoline.

The principle of the classical diesel engine is to convert the reciprocating movements of the crank mechanism (CCM) into mechanical work. The key difference from the ICE running on gasoline is the method of preparation and ignition of the fuel-air mixture.

In diesel, the formation of the mixture takes place directly in the combustion chamber. Accordingly, at the maximum pressure, ignition of the mixture takes place. It's good or bad, we'll figure it out a bit later, and now we'll look at the most interesting.

Two-stroke diesel engine

Such a type of motor is currently of little spread, like a rotary piston engine. It consists of a gas turbine, which is necessary to convert thermal energy into a mechanical and a supercharger. The principle of the latter is to increase power by increasing the pressure. As a consequence, fuel consumption is reduced.

Cylinders in the engine are placed opposite each other in a horizontal position. Actually, why do two-stroke engines have such a name? This is due to the fact that the cylinders work only one revolution of the crankshaft. That is, two cycles are obtained.

The duty cycle of a two-stroke diesel engine is as follows. When the piston descends to its lower point, the cylinder is filled with air. At some point in time, the exhaust valve opens and gases come out through it. At the same time, air enters through the lower windows into the cylinders.

The principle of the two-stroke diesel engine

It is noteworthy that in such ICE uses two types of blowdown: window and valve-slotted. When the cylinder windows are used for intake and exhaust - then this is the window system. If the outlet is adjusted through a special valve in the cylinder, and the inlet through the windows, then the system is valve-slit. This method of purging and purification is most optimal. This is due to the fact that not all air remains in the cylinder. Some of it goes beyond the limits of the motor. The so-called co-current cleaning system ensures optimal removal of combustion products from the cylinders.

A two-stroke diesel engine can operate for quite a long time. This is due to fewer mechanical actions inside the cylinder. So the piston starts its movement from the bottom dead center. At this time, the intake valve and windows are closed. Therefore, the compression process begins. The nozzle is located at the top dead center. Fuel is ignited by hot air. When the piston moves down, the combustion product expands.

Valve-slot blowdown

A significant increase in the efficiency of the motor can be achieved only when the air passes along the axis of the cylinder. If an annular blowdown was used on the first two-stroke engines, which did not give a proper result, then only the valve-slotted was used. Thanks to such a system it was possible to minimize the volume of non-blown areas in the cylinder. The system allowed to close the exhaust valve a little earlier. This approach significantly reduced the loss of fresh charge and improved the boost. Today, the valve-crevice blowdown is used on ships and military equipment.

Advantages of the two-stroke engine

The first such engine was introduced to the world at the same time as the classic 4-stroke diesel engine. Relatively recently there were 2-stroke gasoline engines. A key feature is a small mass. Here you can talk about reducing weight by 40-50% of the classic diesel engine with a turbine. Quite an important characteristic for a modern car, when developers try to reduce the mass of cars as much as possible.

Another advantage is that the device of a two-stroke diesel is somewhat simpler than its colleague. A smaller number of spare parts make maintenance a little easier and cheaper. Although it is possible to argue with the latter, because not all have faced this type of motors. Such a power unit can be reconstructed and repaired with a minimum amount of tools. In fact, this is a simplified version of the internal combustion engine. In addition, the presence of a supercharger can significantly save fuel. Approximately 40-50% of diesel fuel is stored thanks to a two-stroke design. Of course, all motors have their pros and cons. In some cases, deficiencies are more important, since they limit the widespread application.

On the weaknesses

Again, if you list all the shortcomings of the list, then the rotary engine will come to mind. The point is that here it is worth highlighting the following disadvantages:

• High maintenance cost;
• Absence of spare parts;
• Great price for the engine.

The first point is due to the lack of workshops, where they are ready to undertake repair of a two-stroke diesel engine. This is quite natural and logical because not many manufacturers produce serially similar motors, even fewer install them on cars. At a regular maintenance station such a power unit, if done, will cost a lot.

But usually there is just a third minus - there are no necessary spare parts. More precisely, they are, but only under the order. You can wait for them for a month or more. If in large cities and there will be an opportunity to repair such DVS and find spare parts, in the outback this is unlikely to be achieved. These pluses and minuses have this diesel. Well, now consider a few more important details.

A little about the lubrication system

As we have already figured out, this diesel has its strengths and weaknesses. An extremely important part is the lubrication system. It is responsible for the efficient operation of friction parts and their cooling, washing away from deposits. All for a long time already it is known, that for these purposes the engine oil recommended by the manufacturer is used. In our case, everything is exactly the same.

A few words I would like to say about the consumption of lubricating fluid. There is no need to save money. This is due to the addition of lubricant directly to the fuel to ensure the normal operation of rubbing parts. It is quite logical that it will be spent very quickly, and it will need to be added regularly. Moreover, a small oil starvation can disable two-stroke diesel engines very quickly. At least an order of magnitude earlier than the conventional gasoline engine. Therefore, the lubrication system, rather, is weak, rather than a strong side, and this need not be forgotten.

About environmental friendliness

In recent years, engineers are constantly trying to reduce the amount of harmful substances emitted by the exhaust system into the atmosphere. The issue of ecology is quite acute. If the European countries have long introduced environmental standards, then in Russia everything is much worse. As for diesel engines in general, they already for a long time already use special soot filters and low-ash oils, which significantly reduce harmful emissions into the atmosphere.

In our case, it was said that the oil burned in the chamber. This is already a big disadvantage from the point of view of ecology. In addition, part of the fuel-air mixture does not ignite and breaks out. All this, along with the exhaust system, seriously damages the atmosphere. Therefore, two-stroke diesel engines are most expedient to use in military equipment and aviation.

Aviation diesel

These types of motors are widely used in flight technology. Mostly they are used on light aircraft. High power with small dimensions - have become the determining factors in the choice of power units for aircraft. In addition, the presence of supercharging and the lack of ignition played only for the better. The operation of the internal combustion engine stops with the supply of a fuel-air mixture.

It should be noted that the two-stroke marine diesel is not afraid of temperature differences. Moreover, often a large frost is an additional cooling of the ICE, which is very good. All this, along with the use of relatively inexpensive fuel, makes this diesel extremely popular. True distribution is limited by the complexity of installing and maintaining the compressor. In addition, it is necessary to add lubricant to the fuel, which also does not cost cheap. In general, for aviation this is an excellent option, which is due to the above factors.

Increased heat load

We examined the key features of this motor. For example, now you know what the weight of the engine and what are its strengths and weaknesses. But I would like to consider a few more features of the power unit. In particular, we are talking about a cooling system. The fact is that a two-stroke diesel is more heat-loaded than a four-stroke diesel. This is due to the increased frequency of the piston. It turns out that the temperature in the chamber significantly increases. To reduce it, you need effective cooling. If we are talking about aviation, then everything is clear. High speeds and streams of oncoming air do the trick. The same applies to operation in large frosts, when the low ambient temperature is only a plus.

In other cases, liquid cooling is necessary. Usually this is a classical system. The only thing worth paying attention to is the serviceability of all systems. Overheating, even short-term, can lead to wedging or other problems. In any case, the possibility of such an outcome must be excluded.

Resource of a diesel engine

Special attention should be paid to the planned resource of this motor. The fact is that in itself a diesel is less viable than a gasoline power unit. This is due to the use of a kind of fuel. It leaves carbon deposits in the combustion chamber and nozzles. All this significantly shortens the service life. As for two-stroke diesel engines, much depends on operating conditions and timely maintenance. If the oil changes in time, and the engine does not overheat, then 200,000 kilometers can work. For armored vehicles, the resource is much smaller and amounts to about 100,000 kilometers.

Important details

The modern two-stroke diesel engine is characterized by an advanced fuel system. The motor runs smoothly and smoothly. But it was not always so. The mechanical injection pump had its own peculiarities. In particular, there was a separate main line for each injector. This approach, although it had its weak points, was famous for its reliability and high maintainability. Later, the injection pump was improved and became much more complicated. There was a system "Common Rail." In the fuel ramp of this plan, the pressure was maintained at about 2,000 kilograms per centimeter square. The nozzles have become more sensitive to the quality of fuel. Bad fuel led to their rapid failure.

Let's sum up the results

In general, two-stroke diesel engines will develop and improve. Equally, like rotary-piston ICE, they are considered to be unfinished. However, in the near future they will occupy their niche in the automotive industry. Already today they are used in aviation and large industrial and military vessels. This is a reliable and relatively unpretentious motor, which, with proper maintenance, will work properly. At the same time, he is not without problems. For example, the issue of cooling and lubrication is acute. Even more important is the issue of ecology. A complex filtration system is required to achieve environmental standards. For this simple reason, mass production, the use of such motors on all types of cars is difficult and is not yet possible. But improving the exhaust gas cleaning system can solve this problem and will lead to the fact that two-stroke engines will be widely distributed.