OBJECTIVE

The objective of this project is to build and design Iin group of four a micro steam car that will be able to move a minimum distance of 1 meter in the fastest possible time.The focus of the competition is to increase the velocity of the steam car through the use of a energy storing device.

INTRODUCTION

The design of the micro steam car will require the general knowledge and concepts learned in thermodynamics, mechanical design using CAD software and analysis of fluid flow through a turbine. The boiler, the nozzle and the fuel cap are provided by the lab to help standardize the micro steam cars and reduce the complexity of the design. For the correct functionality of the steam car several different constraints must be considered such as the weight, design and energy storing device for the system. By definition, a steam engine also called a heat engine is an external combustion engine where the heat provided by the combustion of the fuel is transformed into mechanical energy which is then transformed into work.

The best type of design is described to have a partial admission impulse design and no pressure change in the rotor blades. By using a micro sized nozzle, the steam only hits the vane at one point on the blade.It has been proven that the angle of the blade should be the same as the nozzle angle since the low pressure from the miniature boiler will cause the absolute and relative velocity to be almost equal.

MATERIAL ANALYSIS

There are two general types of materials used to 3-D print on household printers, ABS and PLA.The properties of these two plastics are outlined in Table 1, below.The machine being used to print the components of the turbine is an external machine that requires 1.75mm PLA filament. PLA filament is more widely used for printing objects with higher dimensional accuracy and is better fit for printing detailed designs. The main difference between ABS and PLA is their glass transition temperature. Generally, ABS is the best selection for designs that require temperature stability however, using an external 3-D printer will allow the flexibility to test different designs more easily. The first turbine prototypes will be in PLA and will be composed of 3 components, the turbine hub, the blade and shaft component and the cover.

SAFETY PRECAUTION

The most crucial part in preventing a fire hazard during the testing on our micro steam car is to ensure that the boiler is properly insulated. By insulating the area around the boiler, we can ensure that the heat from the fire will not melt our chassis.

In order to correctly select the most efficient material for our design, a comparison has been made between different selected materials used for insulation. Since our design has budget limitations, the price of a certain material was also a factor in the team’s decision. Other limitations are related to design where the weight of the material used has an effect on the overall speed of the vehicle. The different materials looked at where wood, plexiglass, cork and aramid fibers such as kevlar, nomex and technora. Before proceeding it is important to note that different constants are looked at as a guidance in our comparison such as thermal conductivity and thermal diffusivity.

FORCE ANALYSIS

The loss of energy could be considered by the difference between the output energy of the boiler and the energy used for the car’s movement.

Certain assumptions are made when it comes to calculate the friction force due to limitations such as not knowing the exact surface material in contact with the wheels and their static and kinematic coefficients. However, static coefficient of friction is calculated from the FBD whereas the coefficient of kinetic friction is assumed by the material of the wheel which is PLA, a kind of plastic so μ_kis assumed to be 0.30 similar to the ABS plastic.

Moreover, other points to consider in energy loss is also the heat loss as steam for the car to push forward because it is not possible to have a 100 % efficiency in power transmission from one shaft to another. Also, other points to consider; loss of energy as heat in the tube and nozzle and all steam hitting the turbine blade at a given time. However, the last two points are assumed to be negligible as to simplify the calculation. Nevertheless, all the mentioned losses seem negligible compared to the friction loss.

Prediction of friction force could be done with accumulated data where one has to calculate the static coefficient of friction in order to find the force to overcome and start the movement. Then, using kinetic coefficient of friction, one can calculate the kinetic friction. Hence, the total friction force is the sum of both.

THERMODYNAMIC ANALYSIS

DESIGN PROTOTYPE