Which type of air filter is most commonly used in on-highway diesel engines?

The most commonly used type of air filter in on-highway diesel engines is the dry type. This preference is primarily due to its efficiency and simplicity. Dry air filters use a pleated paper element to capture dust and debris from the intake air, ensuring that only clean air enters the engine's combustion system. This is crucial for optimal engine performance, as clean air significantly affects combustion efficiency and engine longevity.

Dry filters are also relatively lightweight and economical, making them well-suited for the automotive industry. They operate effectively under a wide range of conditions and are easier to replace or maintain compared to some other types of filters.

In contrast, wet-type filters are less common for on-highway applications as they require a liquid media to trap particulates, which can complicate maintenance and operation. Coalescing filters are primarily used in applications where fuel and oil separation is necessary, typically not for the intake air of diesel engines. HEPA filters are designed for high-efficiency particulate air filtration and are usually reserved for specialized applications where extremely clean air is required, such as in laboratories or cleanrooms, rather than for standard diesel engine use on highways.