Until recently, it seemed impossible. After all, in both engines there is a different compression ratio, that is, different pressure above the piston. In addition, diesel and gasoline engines run on different types of fuel. No wonder, then, that to the question whether it is possible to start the combustion process alternately, everyone will answer “No” !!!
Mercedes F 700 – the first surprise …
So, please imagine the shock when a model about the knowledge so far was presented at the Frankfurt Motor Show in the fall of 2007. That model was the F 700 – a concept car from Mercedes-Benz. Despite its size and weight (length 5180 mm, width 1940 mm, empty weight 1700 kg), the car consumed only 5.3 kilometers at a distance of 100 kilometers Liter. In addition, the F 700 accelerated from 0 to 100 km / h in 7.6 seconds, and the maximum speed was limited to 200 km / h.
This performance was primarily due to the newly developed Diesotto engine. This 1.8-liter four-cylinder engine, 238 hp and a torque of about 400 Nm, had direct injection, turbocharging and … variable compression.
Combustion was the most important part of the new DiesOtto technology. The name itself indicates that the systems developed by Rudolf Diesel and Nicholas Otto were combined.
The highly efficient combustion process was similar to that of a diesel engine, in which the fuel-air mixture itself ignited. The F 700 started as a conventional gasoline engine with a spark plug. At low and medium engine speeds, when there was no need to overcome high driving resistance, the engine worked as an automatic model. With the heavy loads, it drove again like the classic gasoline version.
All this, however, was only in the information provided by the engineers mercedes. When I was asked for more accurate data, I heard a “product secret”.
I considered it a technical curiosity and didn’t bother with it. It was so until 2016.
That’s when the Infiniti VC-Turbo (Variable Compression Turbo) engine was introduced.
It’s the world’s first production series variable-compression engine, and its VC-Turbo technology combines the power of a high-performance 2.0-liter turbocharged petrol engine with… torque The economics of a modern diesel engine. In addition, everything is done without exhaust emissions, as we know from the diesel version.
Commenting on the groundbreaking launch, Roland Krueger, President of Infiniti Motors at the time, said: “The groundbreaking VC-Turbo engine technology is a huge leap forward in engine design. Automotive engineers believe that the real breakthrough in internal combustion technology will be the mastery of variable compression. Infiniti will be The first to bring this technology to the mass market as early as 2018.
How it works?
Infiniti’s VC-Turbo technology is constantly changing, using an advanced multi-lever system to constantly increase or decrease the size of the combustion chamber. Thus, it instantly selects the most appropriate compression ratio based on the detected engine load and driver’s commands. The motor is capable of achieving any compression ratio ranging from 8:1 to 14:1.
The VC-Turbo engine, which develops a maximum power of 272 hp and a torque of 390 Nm, is comparable in performance to six-cylinder gasoline engines. However, it is definitely more economical than them.
The four-cylinder VC-Turbo engine is much quieter and has much lower vibration than conventional internal combustion engines (particularly diesels). It is also lighter and more compact than similar V6 engines.
Infiniti VC-Turbo technology is a huge leap forward in internal combustion engine design, compared to other major innovations such as liquid cooling, fuel injection, catalytic converter and turbocharging.
Since it is really difficult to understand how to change the compression ratio in a sequential motor, we offer the manufacturer’s video.
It is clearly shown that the connecting rod end of the engine is not connected directly to the cortical shaft, but with an additional oval element on the shaft. There is also an additional steel shaft in the engine, which is also connected to this elliptical element on the crankshaft. It is the movement of this rigid shaft that causes the element on the crankshaft to rotate a little. As a result, it still turns with the movement of the shaft, but the connecting rod is lower / higher. The result is a different compression ratio.
At the same time, the fuel injection system also changes.
The solution is great but very complex. However, it has been fantastically received in the automotive world. Unfortunately, in Poland and throughout Europe, the engine is unknown because … Infiniti withdrew from our continent. The reason was the stringent exhaust emissions. While this engine will likely pass EU verification, other engine versions will require design changes. Europe was not a market for the company to invest millions of dollars in modernization. Instead of investing and waiting for a return on investment, Infiniti has pulled out of Europe and… it doesn’t have to wait for a return on investment.
Here is a more explanatory video:
Mazda Skyactiv-X Engine – Could Be Easier…If You Have A Good Base
The essence of the Mazda engine’s operation is the use of an extremely light mixture of air and fuel oil. It is two or three times poorer than the mixtures used to power modern conventional engines. This mixture contains very little gasoline In air that a normal engine cannot ignite with a spark plug.
It all started when Mazda was already using unusually high compression ratios on its Skyactiv series petrol engines as part of its drive to reduce fuel consumption.
The use of these solutions gave rise to the idea of increasing the compression ratio even more, igniting the mixture simply by a very high compression method – similar to what is used in modern diesel engines.
Working change: spark ignition and piezo ignition
The smooth, reliable transition between diesel combustion and spark combustion has been resolved by Mazda through the development of unique SPCCI (Spark Controlled Compression Ignition) technology.
This technology allows the engine to seamlessly switch between conventional ignition mode and compression ignition mode under the influence of high pressure. It achieves this by using a spark plug that works in different ways for both modes.
At Mazda, the candle is always on
The operation of the plug in the pressure ignition mode can be briefly explained as follows: the injection process is divided into two stages. As a result, when switching to the compression ignition mode, two zones of the air-fuel mixture are formed in the combustion chambers.
First, during the intake stroke, a series of injectors fill the combustion chamber with a light mixture of fuel and air (light, that is, a very high ratio of air to gasoline). Secondly, a richer mixture is injected into a strictly defined area in the immediate vicinity of the candle. It can be compared to the icing on a cake – assuming, of course, that the cake is a poor mixture and the fruit is richer.
Due to the very high compression ratio of 16.3:1 used in the Skyactiv gasoline engines, this first load still teeters on the edge of compression ignition. To ignite the mixture at the right time, a small amount of atomic fuel is injected into the area around the candle, which forms an enriched column. When the spark plug sparks, it ignites this local area of the richer mixture, causing a further increase in pressure in the combustion chamber to the ignition point of the smaller mixture.
SPCCI technology operates only under partial engine load conditions. Therefore, only when driving quietly and steadily, when using a light mixture (that is, much more air relative to fuel compared to conventional gasoline engines), can fuel consumption be reduced. However, when the driver needs more power, the engine switches to normal operation, igniting the stoichiometric mixture with an air-fuel ratio of 14.7:1. However, conventional combustion is used only when the engine is heavily loaded and starting at temperatures very low.
The result is 20% lower fuel consumption than Skyactiv-G engines, and 10-30% more torque, depending on the engine’s instantaneous speed. The improvement is particularly marked when the engine is running at low loads, but overall Skyactiv-X technology allows significant fuel savings and lower emissions.
The current Skyactiv-X 2.0 petrol engine is available with either the Skyactiv-MT six-speed manual gearbox or the Skyactiv-Drive six-speed automatic gearbox. It can be purchased on the Mazda 3 and Mazda CX 30 models.
Thus, the term compression ignition engine no longer means the exact definition of a diesel unit.
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