Search Results

Due to compressibility, reactivity, evaporation and mixing, the gas species concentration varies significantly along the intake and exhaust pipes of an engine. An understanding of this behavior is vital to correctly predict catalyst performance because the behavior of a catalyst very much depends on the instantaneous local species concentrations, rather than those in the cylinder. Also, knowing this behavior is more important to assess the effects of exhaust gas recirculation (EGR). The objective of this research is to develop a tool that is capable of predicting the instantaneous species concentration throughout the entire intake and exhaust system, and to lay out a foundation to model catalysts in the near future. This is done by first developing a complete engine cycle simulation model that is able to accurately predict wave dynamics in the piping system. Then, species tracking is accomplished by solving the species conservation equations.

A unique two-stroke engine design is investigated in which fresh mixture is introduced into the cylinder through a valve in the piston crown, and exhausted through peripheral cylinder ports. The engine behaves as a free-piston engine through a portion of the cycle when the piston lifts off the valve seat. The fresh air jet rising along the cylinder centerline effectively displaces the burned gases with little mixing of the two streams. The concept was analyzed by a combination of dynamic cycle simulation and prediction of the in-cylinder flow characteristics by multidimensional modeling. The cycle simulation program considered the dynamics of the piston during its free motion as well as under the kinematic constraints of the crank system. A zero-dimensional thermodynamic model of the cylinder was used to predict cycle pressure and temperature, indicated power, fuel consumption, and flow in and out of the cylinder.

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.

The design of helical Intake ports for swirl generation is a process that has been developed over a number of years through primarily empirical methods. A number of design rules have been established that enable designers to develop ports that approach the state-of-the-art for maximum swirl generation with minimum pressure loss. More recently, computer-aided design (CAD) tools have been introduced that permit geometry and features to be accurately defined by mathematical surface descriptions, and to be parameterized such that derived geometry is updated automatically along with parent features. The author has developed a parametric design approach for helical ports that incorporates the lessons learned from experience into a systematic design procedure. This procedure takes advantage of the current CAD capabilities to expedite the design process and improve the result.

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.