Introduction

Internal combustion engines can be classified into two broad categories: 2-stroke and 4-stroke. The main difference between them lies in the number of piston strokes required to complete a combustion cycle, which directly influences their efficiency, power, and fuel consumption.

When choosing an engine for a motorcycle, boat, vehicle or machinery, one of the main decisions is whether to opt for a 2-stroke or 4-stroke engine. Both systems have advantages and disadvantages in terms of efficiency, power, fuel consumption and environmental sustainability. In this article, we look at their key features to help buyers make an informed decision.

While 2-stroke engines offer greater power in relation to their size, 4-stroke engines stand out for their reliability, lower fuel consumption and lower environmental impact.

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The choice between two-stroke and four-stroke engines has no single definitive answer, as it depends entirely on individual preferences and specific applications. Four-stroke engines are known for their superior durability compared to two-stroke engines, which are noted for their light weight and speed. Although two-stroke engines offer more power, four-stroke engines are more fuel efficient.

Lubrication system: 2-stroke and 4-stroke engines

It is important to understand the lubrication needs of each type of engine before making a choice. Two-stroke engines require an oil-fuel mixture that burns along with the fuel during operation, consuming oil continuously. In contrast, four-stroke engines do not require this mixture, as the lubricating oil returns to the crankcase after use.

The lubrication system plays a fundamental role in distributing oil to moving parts to reduce friction between surfaces, which not only affects engine efficiency but also its durability, maintenance costs and emissions.

Four-stroke engines have gained popularity in power generation due to their cleaner operation, separating intake and exhaust to reduce unburned fuels and released gases.

Main differences between 2-stroke and 4-stroke engines

1. Operating cycle

2-stroke engine: Completes a combustion cycle in two piston movements (one revolution of the crankshaft). This allows it to generate power at each turn.
4-stroke engine: Completes one cycle in four piston movements (two crankshaft revolutions), performing intake, compression, combustion and exhaust in separate phases.

2. Power and performance

2-stroke engines: They are more powerful in relation to their size, since they generate explosions at each crankshaft revolution. This makes them ideal for applications where a high power-to-weight ratio is sought, such as racing motorcycles and outboard engines.
4-stroke engines: Generate power at every other crankshaft revolution, resulting in a more stable and efficient power delivery over the long term. They are more suitable for everyday vehicles, agricultural machinery and automobiles due to their greater durability and fuel efficiency.

3. Fuel consumption and efficiency

2-stroke engines: They have higher fuel consumption due to the fact that part of the air-fuel mixture is lost in the combustion process. In addition, they require mixing oil with gasoline, which increases operating costs.
4-stroke engines: They are more efficient, since they separate the combustion and exhaust cycles, which allows a better use of fuel and a reduction in consumption.

4. Environmental impact and pollutant emissions

2-stroke engines: They are more polluting due to incomplete combustion and the use of oil in the fuel mixture, which generates emissions of hydrocarbons and harmful particles.
4-stroke engines: They are more environmentally friendly, as they burn fuel more efficiently and produce fewer emissions. They also comply with stricter environmental regulations.

5. Maintenance and durability

2-stroke engines: They have fewer moving parts, which facilitates maintenance, but their service life is usually shorter due to faster wear.
4-stroke engines: They are more complex and require periodic maintenance (such as oil changes), but their durability is longer and they show less wear compared to 2-stroke engines.

What is the best option?

The choice between a 2-stroke and a 4-stroke engine depends on the specific use:

If you are looking for power and lightness, as in sport bikes or emergency equipment, the 2-stroke engine may be a better choice.
If efficiency, durability and lower environmental impact are priorities, 4-stroke engines are the ideal alternative for vehicles in continuous use.

We will analyze the impact of 2-stroke and 4-stroke engines in terms of performance and environmental impact according to the type of fuel used: diesel, gasoline and hydrogen.

Comparison of impact by fuel type

Fuel	Performance in 2-stroke and 4-stroke engines	Environmental impact
Gasoline	2-stroke engines: High performance in power, but low in efficiency. 4T engines: Better efficiency, lower consumption.	Pollutant due to the emission of CO₂ and nitrogen oxides (NOₓ). The 2T generate more emissions due to the burning of oil in the mixture.
Gasoil (Diesel)	It is not common in 2-stroke engines, but in 4-stroke engines it offers high performance and better efficiency per liter of fuel.	It produces more particulate and NOₓ emissions, but generates less CO₂ per kilometer than gasoline.
Hydrogen	Applicable only in modified 4T engines, with lower power than gasoline but high thermal efficiency.	Zero CO₂ emissions if from renewable sources. However, it can generate NOₓ at high temperatures.

Which one do specialists recommend?

Experts generally recommend:

4-stroke engines for daily and long-term applications, as they have lower consumption and less environmental impact.
2-stroke engines in cases where a high power-to-weight ratio is required, but with stricter regulations due to higher pollution.
Alternative fuels such as hydrogen or biofuels, especially in 4-stroke engines, due to their lower ecological impact. For a balance between performance and sustainability, a 4-stroke engine with alternative fuels (hydrogen, biogas or e-fuels) is ideal. Although its adoption is limited today, it is the best bet for the future.
For short term: 4-stroke engines with high efficiency gasoline or diesel in industrial applications.
For the medium term: Hybrid or natural gas engines in the transportation and machinery sectors.
For the long term: Hydrogen or electric engines, when infrastructure permits.
Hydrogen is one of the most promising options for the future of internal combustion engines, but its viability compared to electric motors is still a matter of debate among experts. Let’s take a look at it from different angles.

The evolution of internal combustion engines has been remarkable in recent decades, achieving significant reductions in noise pollution, exhaust emissions and fuel consumption, as well as improvements in safety.

In the face of increasingly stringent environmental regulations, manufacturers have adopted two main strategies to reduce pollution: expanding the range of four-stroke engines and optimizing existing models, including improvements to two-stroke engines.

Is hydrogen a viable fuel for internal combustion engines?

Advantages of hydrogen in combustion engines

Zero CO₂ emissions: Unlike gasoline or diesel, hydrogen does not emit carbon dioxide when burned.
Compatibility with current engines: Conventional internal combustion engines can be adapted to use hydrogen with some modifications, such as injection systems and compression ratio adjustments.
Fast recharge vs. electric batteries: Unlike electric vehicles, hydrogen tanks can be refueled in minutes, similar to fossil fuels.
Greater autonomy: It can offer a greater range than electric vehicles, especially in trucks, boats and heavy machinery.

Hydrogen challenges for combustion engines

Low energy efficiency:
- Hydrogen engines have an efficiency of 30-40%, similar to that of gasoline engines, while a fuel cell (hydrogen electric) exceeds 60%.
- Electric motors reach efficiencies of 90%, making them more energy efficient.
Green hydrogen production:
- Most of today’s hydrogen comes from natural gas (gray hydrogen), which generates emissions.
- To be truly sustainable, green hydrogen produced with renewable energy is needed, which is still expensive.
Limited infrastructure:
- Hydrogen stations are scarce and expensive to develop. In contrast, the infrastructure for electric vehicles is growing rapidly.
Formation of nitrogen oxides (NOₓ):
- Although hydrogen does not emit CO₂, combustion in conventional engines generates NOₓ, an air pollutant that requires aftertreatment systems.

Conclusion

4-stroke engines are more efficient and durable, while 2-stroke engines offer more power and acceleration in a smaller size and weight. 2-stroke engines are ideal for lightweight, high-performance equipment, but require more maintenance. 4-strokes are preferred in vehicles and machinery because of their lower fuel consumption and longer service life.