Vehicular engine design pdf free download

Also manufacturing aspects are peculiar to these engines because of their small size. This implies rotating parts to be machined with very high precision.

The University of Padova is undergoing a project aimed at developing small turbojet engines for research and educational purposes. The ultimate goal of this project is to acquire the necessary competency to design, manufacture, operate and test such engines. These features were achieved according to some basic thermodynamic and mechanical rules, described as follows: 1. Select a simple open Brayton—Joule thermodynamic cycle in order to make the overall design and system architecture as simple as possible, and thus avoid any cycle sophis- tication, such as internal regeneration, air bleeding, blade cooling, etc.

Adopt a turbine-inlet temperature smaller than K. Use standard-technology turbomachinery and rotordynamics design, without any var- iable geometry device and using standard ball-bearings to support the core engine. Design procedure of the turbojet engine The following are the steps that we followed in the development of the turbojet. Thermodynamic-cycle design and analysis A Brayton—Joule cycle simulator was used to predict the performance of the turbojet engine; the simulator was implemented as described in detail in [6].

In the thermodynamic model, the following assumptions were made: — Ambient pressure and temperature of air are Therefore, a pressure ratio of 2. The other relevant parameters of the cycle are reported in Table 1.

There- fore, a new simulation of the engine cycle was carried out and a redesign of the compressor was performed accordingly. This procedure was repeated until convergence from cycle analysis and component performance was successfully achieved. The predicted maps of the compressor are illustrated in Fig. The compressor impeller was obtained from one piece of Aluminium Alloy Ergal using a 5-axis numerical control machine. The intake and compressor casing are two separate items made of an aluminium alloy.

The machining of the rotor casing had to be highly accurate. Tip clearances have been kept around 0. Combustion-chamber design As one might expect, the combustion chamber design is a very complicated task in small gas-turbine engines, being its size limited by the strong coupling issues regarding the com- pressor and turbine, typically constructive limitations on shaft length and diameter. This layout is illustrated in Figs. Computer representation of the compressor assembly.

Photos of the manufactured compressor. The mixing is augmented by the presence of turbulators, and the recirculation in the Fig. Predicted compressor map. Computer representation of the combustion-chamber. Photos of the constructed combustion chamber. The design of the combustor was performed following the rules dictated by Lefebvre [15]: Two main issues have been considered and lead to a complicated design, i.

As is well known, stabil- ity limits for sustained combustion with respect to fuel-to-air ratio are wide, but these lim- its are much narrower for ignition. Therefore, good ignition characteristics depend greatly on the fuel-injector design and the achievable atomization quality. A well-atomized or evaporated fuel preferably close to the stoichiometric fuel-to-air ratio is required in the primary zone, especially at low rotational speeds, when air temperature and pressure at the inlet to the combustion chamber are almost ambient.

This is especially detrimental to ignition performance because of the large ignition heat-loss and the very poor fuel- atomization quality that can actually be achieved. For these reasons, fuel pre-evaporation provided the best solution. The design consists of a fuel pre-evaporator manifold located within the combus- tion chamber. Because the fuel and the combustion chamber are cold at start-up, the fuel cannot be pre-evaporated unless it is preheated to its high evaporation temperatures just before ignition, which is cumbersome.

The solution was to use a natural-gas fuel for start- up and ignition. The latter was accomplished by a discharge spark-ignition unit developed in-house. A kerosene fuel was then selected for operating this turbojet engine after start-up. At minimum idle speed, the transfer to kerosene fuel is initiated through the same gas man- ifold, using synchronized valves.

The already hot gases in the combustion chamber then preheat the fuel in the manifold to a high evaporation level before it enters the combustion chamber.

Safety in fuel handling and engine operation has been a serious design issue. Finally, since kerosene at high temperatures tends to produce coke as a result of the thermal cracking of hydrocarbons, we were particularly worried about coke layer formation on the inner wall of the evaporators.

The use of kerosene did require the addition of a booster pump for fuel pressurization. Ample margins in temperature thermal stress and rotor speed component loadings have been provided to ensure a long life, particularly for the hot- section components. It consists of a nozzle row and a 0. They were actually derived using a prescribed-curva- ture turbine-blade method [19].

The preliminary design was carried out using a one-dimensional procedure at the mean radius of the turbine, following the well-known procedure illustrated by Horlock [18], and using loss correlations given by Craig and Cox [17], and the deviation correlation expressed by Ainley and Mathienson [20].

The nozzle row featured 25 blades having con- stant stagger angles with radius, while a free-vortex criterion was used to determine the angles at various radii of the 29 rotor blades Fig. In this way, the loading on the blade was increased with respect to conventional design practice. The nozzle blade row was constructed using refractory steel S.

Computer representation of the turbine rotor left and nozzle vanes right. The compressor and turbine are connected using a V steel shaft supported by a couple of preloaded ball bearings. The rotor-bearing module was accu- rately aligned and balanced with all other components in order to control the tip clear- ances of both compressor and turbine. Both bearings are lubricated and cooled with oil fed from the externally-mounted tank by a tube through the compressor casing.

This lube-oil system is of the total-loss type. Photos of the manufactured turbine. Before start-up, when no pressure is available, oil is fed manually. Discharge nozzle: Computer representation left and manufactured component right. Two-dimensional drawing of the designed turbojet dimensions in mm. Computer representation of the designed turbojet.

Assembly Design A modular design concept has been maintained throughout the entire engine. Engine validation and durability. Engine development process. Determining displacement. Engine configuration and balance. Cylinder block and head materials and manufacturing. Block layout and design decisions. Cylinder head layout design. Block and head development. Engine bearing design. Engine lubrication.

Engine cooling. Gaskets and seals. Pistons and rings. Crankshafts and connecting rods. Camshafts and the valve train. Back Matter Pages About this book Introduction The mechanical engineering curriculum in most universities includes at least one elective course on the subject of reciprocating piston engines. The majority of these courses today emphasize the application of thermodynamics to engine ef?

There are several very good textbooks that support education in these aspects of engine development. However, in most companies engaged in engine development there are far more engineers working in the areas of design and mechanical development.

University studies should include opportunities that prepare engineers desiring to work in these aspects of engine development as well.

My colleagues and I have undertaken the development of a series of graduate courses in engine design and mechanical development.