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The growing usage of Unmanned Aerial Vehicles (UAVs) for aerial surveillance and reconnaissance in military applications calls for lightweight, reliable powerplants that burn heavy distillate fuels. While mass-produced engines exist that provide adequate power-to-weight ratio in the low power class needed for UAVs, they all use a spark-ignited combustion system that requires high octane fuels. Southwest Research Institute (SwRI) has embarked upon an internal research effort to design and demonstrate an engine that will meet the requirements of high power density, power output compatible with small unmanned aircraft, heavy-fuel combustion, reliable, durable construction, and producible design. This effort has culminated in the successful construction and operation of a demonstrator engine.

Computer based analytical design techniques are transforming the engine design process. Analytical tools allow faster and more accurate design optimization. The design process is also shortened because the electronic transfer of files permits the design to be worked concurrently by engineers working with different analysis packages or on various parts of the design. Prototype parts and tooling can be made directly from the Computer-Aided Design (CAD) by various rapid prototyping methods. The analytical design techniques can also permit a highly optimized design with less possibility of corrections being necessary in the development stages. This paper reviews these new design techniques and examines how they can be used to improve the design technique. The following design tools are discussed.

The cylinder head of a direct-injection diesel engine has to perform many functions. It must bring charge air to the cylinder and exhaust gas from the cylinder, with minimum pumping loss and required swirl and other properties of charge motion. It must provide a mounting for the injector, seal the combustion gases and maintain acceptable temperatures of the components. The cylinder head is therefore a crowded and complex component. This paper discusses the options that can be applied to cylinder head design of four-stroke, direct-injection diesel engines with head-mounted valves. Intake ports generate swirl in two modes; the directed mode and the helical mode. Intake ports generate swirl most efficiently when the swirl generated by the directed mode is about 30 percent of the total. It is possible to measure the magnitude of the directed and helical modes of swirl generation by special flow bench tests.