A modern diesel engine is an efficient device with high efficiency. If earlier diesel engines were put on agricultural machinery (tractors, combines, etc.), then now they are equipped with ordinary city cars. Of course, someone associates a diesel engine with black smoke from an exhaust pipe. For some time it was, but now the exhaust system has been modernized, and there are practically no such unpleasant consequences. Let's look at two-stroke diesel engines and their features.
Some general information
A key feature of a diesel engine is its increased efficiency. This is due to a greater extent to fuel, which is 15% more efficient. If you look at fuel at the molecular level, here we will see a long chain of carbons. Due to this, the output of diesel fuel is slightly higher than gasoline.
The principle of operation of a classic diesel engine is to convert the reciprocating movements of the crank mechanism (KShM) into mechanical work. The key difference from gas-fired ICE is the method of preparation and ignition of the air-fuel mixture.
In a diesel engine, the formation of a mixture occurs directly in the combustion chamber. Accordingly, at maximum pressure, the mixture ignites. For better or worse, we'll figure it out a bit later, and now let's look at the most interesting.
Two stroke diesel engine
This type of motor is currently not widespread, as is a rotary piston engine. It consists of a gas turbine, which is necessary to convert thermal energy into mechanical energy and a supercharger. The principle of the latter is to increase power by increasing pressure. As a result, fuel consumption is reduced.
Cylinders in the engine are located opposite each other in a horizontal position. Actually, why are two-stroke engines so named? This is due to the fact that the cylinders operate in only one revolution of the crankshaft. That is, two measures are obtained.
The duty cycle of a two-stroke diesel engine is as follows. When the piston lowers to its lower point, the cylinder is filled with air. At a certain point in time, the exhaust valve opens and gases escape through it. At the same time, air enters the cylinders through the lower windows.
The principle of operation of a two-stroke diesel engine
It is noteworthy that in such ICE two types of purging are used: window and valve-slot. When the cylinder windows are used for intake and exhaust, this is a window system. If the outlet is adjusted through a special valve in the cylinder, and the inlet through the windows, then the valve-slot system. This method of purging and cleaning is most optimal. This is due to the fact that not all air remains in the cylinder. Some of it goes beyond the motor. The so-called direct-flow cleaning system ensures optimal removal of combustion products from the cylinders.
A two-stroke diesel engine can run for quite a long time. This is due to fewer mechanical actions inside the cylinder. So the piston begins its movement from the bottom dead center. At this time, the inlet valve and windows close. Therefore, the compression process begins. The nozzle is located at top dead center. Fuel ignites from hot air. When the piston moves down, the combustion product expands.
Valve Slit Purge
A significant increase in motor efficiency can only be achieved when air passes along the axis of the cylinder. If the first two-stroke engines used ring blowing, which did not give the desired result, then in the future only valve-slotted was used. Thanks to this system, it was possible to minimize the volume of non-blown areas in the cylinder. The system allowed a little earlier to close the exhaust valve. This approach significantly reduced the loss of fresh charge and improved boost. Today, valve-slot purge is used on ships and military equipment.
Advantages of a two-stroke motor
The first such engine was introduced to the world at the same time as the classic diesel 4-stroke engine. Relatively recently appeared 2-stroke gasoline engines. The key feature is light weight. Here we can talk about reducing weight by 40-50% from a classic diesel engine with a turbine. Quite an important characteristic for a modern car, when developers are trying to reduce the mass of cars as much as possible.
Another advantage is that the two-stroke diesel device is somewhat simpler than its counterpart. Fewer parts make maintenance easier and cheaper. Although the latter can be argued, after all, not everyone has come across this type of engine. Such a power unit can be reconstructed and repaired with a minimum amount of tool. In fact, this is a simplified version of an internal combustion engine. In addition, the presence of a supercharger can significantly save fuel. Approximately 40-50% of diesel fuel is retained due to a two-stroke design. Of course, all motors have their pros and cons. In some cases, disadvantages are more important, since they are the ones that limit the widespread use.
About weaknesses
Again, if you list all the shortcomings with a list, then the rotary engine will come to memory. The fact is that it is worth highlighting the following disadvantages:
- high cost of service;
- lack of spare parts;
- Great price for the engine.
The first point is due to the lack of workshops where they are ready to take on the repair of a two-stroke diesel engine. This is quite natural and logical, because not many manufacturers produce such engines in series, even fewer install them on cars. At a regular service station, such a power unit, if they do, will be expensive.
But usually the third minus immediately arises - there are no necessary spare parts. More precisely, they are, but only on order. You can wait for them for a month or more. If in large cities there will be an opportunity to repair such an internal combustion engine and find spare parts, then it is unlikely to do this in the outback. These are the pros and cons of this diesel engine. Well, now consider a few more important details.
A little bit about the lubrication system
As we have already figured out, this diesel engine has its own strengths and weaknesses. An extremely important part is the lubrication system. She is responsible for the effective work of the rubbing parts and their cooling, washing from soot. Everyone has long known that engine oil recommended by the manufacturer is used for these purposes. In our case, everything is exactly the same.
I would like to say a few words about the consumption of lubricating fluid. There is no need to wait for savings. This is due to the addition of lubricant directly to the fuel to ensure the normal operation of the rubbing parts. It is logical that it will be spent very quickly, and it will need to be added regularly. Moreover, a slight oil starvation can disable two-stroke diesel engines very quickly. At least an order of magnitude earlier than conventional gasoline ICE. Therefore, the lubrication system is rather weak than strong, and this should 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 environmental standards have long been introduced in European countries, in Russia everything is much worse. As for diesel engines in general, they have been using special particulate filters and low-ash oils for quite some time now , which significantly reduce harmful emissions into the atmosphere.
In our case, it was said that the oil burns in the chamber. This is a big minus from an environmental point of view. 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 suitable for use in military equipment and aircraft.
Aviation diesel
These types of engines are widely used in flight technology. Most used on light aircraft. High power with small dimensions - became the determining factors when choosing power units for aircraft. In addition, the presence of boost and the absence of ignition played only for the better. The operation of the engine stops with the supply of the fuel-air mixture.
It is worth noting that a two-stroke marine diesel engine is not afraid of temperature differences. Moreover, often a large frost is an additional cooling of the internal combustion engine, which is very good. All this, along with the use of relatively inexpensive fuel, makes this diesel engine extremely popular. True distribution is limited by the complexity of installation and maintenance of the compressor. In addition, lubricant must be added to the fuel, and this is also not cheap. In general, for aviation this is an excellent option, due to the above factors.
Increased heat load
We examined the key features of this motor. For example, now you know how much the engine weighs and what its strengths and weaknesses are. But I would like to consider a few more design features of the power unit. In particular, we will talk about the cooling system. The fact is that a two-stroke diesel engine is more heat-loaded than a 4-stroke one. This is due to the increased frequency of the piston. It turns out that the temperature in the chamber increases significantly. To reduce it, effective cooling is necessary. If we are talking about aviation, then everything is clear. High speeds and streams of oncoming air do their job. The same applies to operation in large frosts, when a low ambient temperature is only a plus.
In other cases, liquid cooling is necessary. This is usually a classic system. The only thing worth paying attention to is the serviceability of all systems. Overheating, even briefly, can lead to jamming or other problems. In any case, the possibility of such an outcome must be ruled out.
Diesel resource
Special attention deserves the planned resource of this motor. The fact is that a diesel engine itself 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 reduces the service life. As for the two-stroke ICE on a diesel engine, much depends on the operating conditions and timely service. If the oil changes on time, and the motor 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
A modern two-stroke diesel engine is characterized by an advanced fuel system. The motor runs quietly and smoothly. But it was not always so. Mechanical fuel injection pump had its own characteristics. In particular, a separate line went to each nozzle. This approach, although it had weaknesses, was famous for its reliability and high maintainability. Later TNVD improved and became much more difficult. The "Common Rail" system appeared. In the fuel rail of such a plan, a pressure of about 2 thousand kilograms per centimeter squared was maintained. Nozzles have become more sensitive to fuel quality. Bad fuel led to their rapid failure.
To summarize
In general, two-stroke diesel engines will develop and improve. As well as rotary piston ICEs, they are considered unfinished. However, in the near future they will occupy their niche in the automotive industry. Already today they are used in aviation and on 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 burning issue is cooling and lubrication. Even more important is the issue of ecology. A sophisticated filtration system is needed to achieve environmental standards. For this simple reason, mass production, the use of such engines on all types of cars is difficult and is not yet possible. But improving the exhaust gas treatment system can solve this problem and lead to the fact that two-stroke engines will be widespread.