longstroke

Longstroke refers to a design characteristic of internal combustion engines in which the piston travel distance, or stroke, is long relative to the bore diameter. The stroke is the linear distance the piston travels between top dead center and bottom dead center. A long-stroke layout increases the crankthrow-to-bore ratio, giving greater leverage on the crankshaft. This typically yields higher torque at low to mid-range engine speeds and can improve mechanical efficiency at those speeds, particularly in diesels and other slow-running engines. A longer stroke also tends to produce a larger displacement and can enhance expansion in some designs. However, it increases the engine’s overall length and raises mean piston speed at a given RPM, which can limit the maximum engine speed due to higher piston velocity and greater side forces.

Applications and trade-offs: Long-stroke configurations are common in heavy-duty diesel engines used in trucks, ships, and stationary power because of their torque characteristics and durability at low speeds. They contrast with short-stroke or square engines, which favor high-revving operation and higher peak horsepower. The main trade-offs are a larger physical size, potentially higher friction and wear, and reduced capability for very high RPM without specialized engineering.

Design considerations: Realizing a long-stroke engine involves balancing bore size, crankshaft strength, lubrication, and thermal management. Piston design, bearing geometry, and valve timing are optimized to manage increased side thrust and heat. Manufacturers tailor stroke-to-bore ratios to meet the intended service profile, life requirements, and operating envelope.