In the world of engineering and mechanics, misconceptions often arise that grow up in legends faster than official technical bulletins can be produced. 8-stroke engineIf you have encountered this phrase in a conversation of mechanics or on the pages of dubious forums, we hasten to disappoint you: in the classical understanding of thermodynamics, such an aggregate does not exist.
But the idea of multicycle systems is not without its meaning. Engineers have been looking for centuries for ways to improve fuel efficiency and reduce emissions by experimenting with cycles. Why did the number eight come to be used in the context of internal combustion engines? The answer lies in trying to combine the benefits of diesel and gasoline cycles, and in specific designs with split combustion chambers.
In this article, we will explore the physics of the process, explain why a standard Otto or Diesel cycle is limited to four cycles, and consider real-world engineering solutions that could theoretically be called “eight strokes” because of the complexity of their work.
Physics of the process: why exactly four bars?
To understand the impossibility of a classic 8-stroke engine, we need to go back to the basics of thermodynamics: Any operation of an internal combustion engine (ICE) is based on converting heat into mechanical energy. The standard cycle includes four mandatory stages: let-in, compression, work-in and releaseThese processes are physically necessary to update the charge in the cylinder and do useful work.
Trying to increase the number of bars to eight in one cylinder would lead to a catastrophic drop in efficiency. Imagine: if you stretch the process by 8 movements of the piston, then for each working move there would be 7 idle or preparatory moves. Mechanical losses The friction and inertia would eat up all the power gain instantly, and the engine would become bulky, heavy, and incredibly inert.
However, there are concepts where cycles are split between different cylinders, such as in counter-current purging engines or in Atkinson/Miller systems, the timing phases are shifted so that the effective compression cycle is different from the expansion cycle, which creates the illusion of "extra cycles," but physically the piston still does the same movements.
⚠️ Attention: Attempting to independently convert the four-stroke engine into an 8-stroke one by changing the gas distribution phases will lead to the destruction of the crank-shaking mechanism due to increased resistance and lubrication disturbance.
So, in classical mechanics, 8 bars in one cylinder is a dead end of evolution, but engineers wouldn't be engineers if they didn't try to circumvent the limitations of physics with a trick.
The classic 8-stroke cycle in one cylinder does not make practical sense due to a sharp decrease in efficiency and an increase in mechanical losses.
Where the "eighth" bars hide: complex cycles
If you've heard the term 8-stroke engine, it's probably a combination of systems, and in these units, the intake, combustion and exhaust can be spaced out in time and space. split-combustion chambers Exhaust energy recovery systems that formally add work steps.
Of particular interest are the boxed engines with a unique lubrication and gas exchange system, where the cycles in different cylinders overlap each other, creating a total continuity effect that theorists sometimes jokingly call multi-stroke. Stirling engines with external heat supply, where the number of phases of movement of working pistons can be large, but it is no longer an engine in its pure form.
Some experimental designs used a circuit where combustion took place in two stages: pre-ignition of the poor mixture and main combustion of the enriched one. This allowed for control of detonation and increased efficiency by simulating an extended working cycle. In fact, it added intermediate stages to the combustion cycle.
The secret of the “eight bars” in diesel engines
In some large marine diesel engines, the combustion and expansion process is artificially stretched due to late injection and complex camera geometry, which is sometimes called a “pseudo-multi-stroke” mode of operation in the technical literature.
It's important to understand that even in the most complex systems, we're talking about modifying the four basic processes, not creating fundamentally new physical clocks. Engineers are just using the time and volume of the cylinder more efficiently.
Comparison of cycles: Otto, Diesel and pseudo-multi-strokes
For clarity, let’s look at how standard cycles differ from those that attempt to simulate complex multi-stroke work, and the table below compares the key parameters that affect efficiency and the ability to extend the cycle.
| Parameter | Otto Cycle (Benzin) | Diesel cycle | The Atkinson/Miller Cycle |
|---|---|---|---|
| Compression | Same with extension | High, compression ignition | Less than expansion |
| Expansion | Standard. | Standard. | Increased (effective 5th bar) |
| Efficiency | Medium. | Highly | Maximum for ICE |
| Application | Passenger cars | Trucks, boats | Hybrids (Toyota, Honda) |
As you can see from the table, the Atkinson cycle, which is widely used in modern hybrids, is already beyond the classic "four": here the piston stroke is longer than the compression stroke. This is achieved by later closing the intake valves. In fact, part of the mixture is pushed back into the intake manifold, which reduces the effective compression ratio, but allows you to maximize the energy of gas expansion.
Some engineers believe that adding turbocharged systems, where exhaust energy is transferred back to the crankshaft through hydraulics or mechanics, can be considered another "tact" of useful work. If you count all the stages of energy conversion, including recovery, you can collect 8 stages, but technically it is still four-stroke base with recycling systems.
When choosing an Atkinson cycle car, remember that it has less specific power, but is much more economical in the urban cycle due to the effect of “long” expansion.
Myths about 8-cylinder engines and strokes
Often confusion arises from a misunderstanding of the cylinder configuration. V8 engine It's an eight-cylinder unit, but each one runs a standard four-stroke cycle, and the crankshaft gets 4 strokes per revolution (in the right order of operation), which ensures smoothness but doesn't change the thermodynamics of the process in a single cylinder.
There is a persistent myth that the V8 somehow clocks in a special way, creating an "eight-stroke" power effect. This is not true. The order of operation of the cylinders (for example, 1-5-4-2-6-3-7-8) only evenly distributes the load on the crankshaft. The crank-shaking mechanism It's still classic.
Another misconception is that two-stroke engines, which cycle in one crankshaft rotation (two strokes of a piston), would seem to combine two two-stroke cylinders into a box, you get 4 bars? No, you get just paired power. The mathematics of cycles is inexorable: for full charge and combustion renewal, you need certain time intervals, which are dictated by the speed of combustion of fuel.
- 🚀 Myth: The 8-stroke engine is more powerful than the four-stroke one. Reality: At the same volume, the four-stroke uses fuel more efficiently.
- ⚙️ Myth: Eight-stroke engines are quieter. Reality: The complexity of the design would increase the noise from the additional gas distribution mechanisms.
- 🛢️ Myth: They don't require butter. Reality: Any friction requires lubrication, regardless of the number of strokes.
Destroying these myths helps us to better understand the real structure of technology and not to be led by marketing tricks or pseudoscientific theories of “perpetual motion machines”.
Engineering attempts to create multicycle systems
Despite skepticism, attempts to create a split-phase engine (which theoretically brings it closer to a multi-stroke engine) have been ongoing. split-cycle In this scheme, some cylinders are responsible only for compressing air, while others are responsible for expanding gases after combustion.
In such a system, you can count many "strokes": air intake, transfer to the compression cylinder, compression, transfer to the working cylinder, injection, combustion, expansion, exhaust. If you count the gas transfer between the cylinders as separate bars, you can easily count 6 and 8 stages. However, such a system is extremely difficult to seal and control thermal regimes.
Another example is Wankel's rotary-piston engines, which, although they are considered rotary, also have 4 phases, but they occur in different sectors of the body simultaneously, and attempts to combine piston and rotary principles in one hybrid plant also produced monstrous designs that were jokingly called "multi-stroke."
☑️ Signs of a complex cycle system
To date, none of these schemes have been widely adopted due to low reliability and high cost of production, and the simplicity of the four-stroke cycle remains unmatched in terms of price-performance.
The future of ICE: hybridization as a new “tact”
The modern automotive industry is moving towards electrification, and that's where the answer to the question of "eighth bar" lies. ICE operates in a narrow range of speedsThe electric motor takes over the acceleration and recovery functions.
You could say that electric propulsion adds a new "stroke" to the overall operation of the car's power plant. When you brake, the energy returns to the battery (conditional 5th stroke), when you start, electricity runs (6th stroke), and the ICE is turned on only for generation or cruising speed. The control system for such a hybrid installation (HSD, e-CVT) is more complex than any mechanical 8-stroke project.
It is also worth mentioning technology. variable-compression The engine can physically change the height of the cylinder block as it adapts to the load, and this dynamic change in geometry is aerobatics engineering that makes the notion of static clockwork obsolete.
⚠️ Warning: Complex hybrid systems require skilled maintenance, and errors in software or sensors can cause the engine to go into emergency mode.
Thus, evolution did not go the way of increasing the number of mechanical clocks, but the way of intelligent energy management and combination of different types of motors.
Frequently Asked Questions (FAQ)
Is there really an 8-stroke engine?
In the classical sense (one cylinder, 8 piston strokes per cycle) — no, it is thermodynamically impractical. There are complex split-cylinder circuits or hybrid systems that can be formally decomposed into 8 stages of operation, but there is no commercial name for the 8-stroke engine.
Why is the V8 called an eight-cylinder instead of an eight-stroke?
Because the number 8 is the number of cylinders (combustion chambers), not the number of cycles. Each cylinder in a V8 engine operates on a standard four-stroke cycle (intake, compression, stroke, exhaust).
Which engine is more efficient: two-stroke or four-stroke?
The four-stroke engine is more efficient in terms of fuel consumption and ecology, as it has better cylinder cleaning and less fuel loss. two-stroke more powerful per unit volume, but "gluster" and dirtier.
Can I convert a regular motor into a multi-stroke motor?
Theoretically, it is possible to change the phases of gas distribution (Atkinson cycle), but it is impossible to turn a four-stroke into a full 6 or 8-stroke without a complete restructuring of the crank-shaking mechanism and valve system.
In conclusion, the term 8-stroke engine remains an interesting curiosity in the world of technology, a reminder that engineers never stop looking for ways to improve, even if those paths lead to a dead end. The reality dictates its rules: whoever can use four-stroke efficiently, complementing them with electric traction and smart electronics, wins.