Which type of hydraulic injector features a single hole?

The pintle type of hydraulic injector is characterized by having a single hole for fuel spray. This design allows for a more directed and controlled flow of fuel into the combustion chamber, which is essential for efficient combustion in various applications, including engines. The single hole provides a focused jet of fuel, enhancing atomization and mixing with air, which improves the combustion process.

In contrast, multi-port injectors typically have multiple holes to distribute fuel more evenly across a broader area, while jet injectors may refer to designs where fuel is atomized through various means, sometimes involving multiple holes as well. The other options do not specifically refer to a type of injector designed with the distinct feature of a single hole for injecting fuel, which is why the pintle is the correct choice for this question.