What is the difference between high-speed diesel engines and low-speed diesel engines?

[VonRose]

High-speed diesel engines and low-speed diesel engines have the following differences: 1. Speed: Low-speed diesel engines have a speed of 60120 rpm; high-speed diesel engines have a speed of 6002250 rpm. 2. Cylinder bore: Low-speed diesel engines have a cylinder bore of 350900 mm; high-speed diesel engines have a cylinder bore of 98185 mm. 3. Single-cylinder power: Low-speed diesel engines have a single-cylinder power of 5673855 kW; high-speed diesel engines have a single-cylinder power of 915127 kW. A diesel engine is an internal combustion engine that uses diesel as fuel. During operation, the diesel engine draws air into the cylinder, which is highly compressed due to the movement of the piston, reaching a high temperature of 500~700°C. Then, fuel is injected in a mist form into the high-temperature air, mixing with it to form a combustible mixture that ignites and burns automatically.

[LincolnDella]

Recently, I've been researching various types of diesel engines and found that the main difference between high-speed and low-speed diesel engines lies in their RPM range. High-speed engines typically operate above 1000 RPM, such as those commonly used in trucks—they accelerate quickly, are compact in size, and are suitable for vehicles requiring frequent speed changes. Low-speed engines generally run below 300 RPM and are most favored for marine use; although they rotate slowly, they produce exceptionally high torque, making it effortless to push massive ships. Their structures also differ: high-speed engines have shorter piston strokes and higher operating frequencies, while low-speed engines have opposite bore-to-stroke ratios, resulting in bulkier but longer-lasting designs. Fuel adaptability varies too—low-speed engines can even burn heavy fuel oil, saving significant costs.

[KayleeMarie]

I've worked with quite a few construction machines and compared two types of diesel engines. The high-speed variant is most commonly found in tractors or excavators, producing a sharper sound during operation and noticeable vibrations at higher RPMs. However, it excels in responsiveness, handling slopes and heavy loads with ease. The low-speed type, on the other hand, is the old reliable in port cranes or ocean-going vessels, operating as steady as a mountain with minimal vibration and a deep, muffled noise. In terms of fuel consumption, low-speed engines save about 20% more fuel than high-speed ones during continuous operation, though they require a ten-minute warm-up. Maintenance is also interesting: high-speed engines wear out parts faster but are easier to replace; low-speed engines can go five years between major overhauls, though disassembly requires a crane.

[SanMaddox]

Driving trucks for twenty years, I deal with high-speed diesel engines every day. These machines can rev up to 4000 RPM, and paired with turbocharging, they perform exceptionally well on highways. Their size is half that of low-speed models, making them a perfect fit for truck engine bays. The downside is their higher fuel consumption, especially when fully loaded or climbing hills. Low-speed engines are a completely different story—I touched one during a marine engine exhibition, where the tachometer maxed out at just 200 RPM, but a single cylinder was as big as a washbasin! The low RPM translates to an ultra-long lifespan, with thirty years of service on ships being nothing unusual. There's also a difference in lubrication systems: high-speed engines require premium synthetic oil, while low-speed engines can manage with regular mineral oil.