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Small-Scale Two-Stroke Compression Ignition Engine
Mechanical Design A: Upper Second Class
Team Size: 3 Mechanical Engineers
My Responsibilities: CAD (Fusion 360), CAM & Machining Simulations (Fusion360), Manufacturing Report (DFM and Assembly Operations Sequence), Machining Simulations (Fusion360), Material Selections (Granta Edupack), Calculations on Porting and Port Arrangements, and Engineering Drawings.
2nd Year Mechanical Engineering
2022
The approach in this project is to design a small-scaled two-stroke, compression ignition engine for use in an Unmanned Aerial Vehicle (UAV) to be used for exploration missions. The engine must power for at least 15 minutes of flight, with 0.06 mhp at a speed of approximately 12,000 rpm. This would then be scaled up to produce 50,000 units.
This project offered me a thorough perspective on the importance of cost, safety, and performance in engineering design.
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BRIEF OVERVIEW
Design
Assembly drawings of the Engine
Drawings of Piston Heights for Various Port Openings
1. Drawing of piston height during intake port openings and closings (when crank is at 45° and
135°).
Several design changes were made throughout the project, including changing the diameter of the shafts, in order to integrate more standard parts into the engine. The non-standard components are mainly manufactured using sand casting as a primary process and a combination of mostly turning, milling and drilling as secondary processes. Specifically, the engine casing would be sand casted, heat treated, then milled and drilled. For the assembly of the engine, sub-assemblies involving the cylinder head, piston and crankshaft and the carburettor would be made. These would then be generally assembled, with standard screws used to fix the parts together. The materials chosen for the parts were carefully selected using the Granta Edupack 2021 software and a documented step-by-step process was carried out for the piston. This involved finding the property constraints of the part and screening candidate materials to fit the requirements. A material index was used to limit the mass of the part. The final material chosen was cast iron which would be sourced locally. An eco analysis was carried out on the cast iron piston, with cast iron being compared to stainless steel. In the part life, cast iron was more sustainable as it consumed less energy and released less CO2 .
Design Validation
Basic Engine Parameters
A bore-stroke ratio of 0.9 were chosen, while the engine displacement were determined as 6.4 mm, the swept volume of the piston chamber was 706 mm3. The operating compression ratio of the engine is 16:1, and 8:1 for its starting postion, hence h1 and h2 were calculated as 0.6 mm and 1.3 mm respectively.
Component Manufacturing
Overall process plan for all nonstandard components: