Designing a single cylinfer 4 stroke engine for a moped

In summary, the moped engine that the person is designing will need to be able to power a scooter at a maximum speed of 70km/hr. The engine will also need to be able to run at a speed of 40km/hr.
  • #1
webster7
3
0
Hey
I currently have a project to design an engine and I have chosen to design it for a moped. My research so far has brough me to this:

The highest engine rating of a moped is 130cc in Kansas, while most states require moped to be less than 50cc.1 For this project, we will consider a moped that needs an engine capacity of 125cc, which is 0.125 liter. The speed at which mopeds are allowed to run varies between 20mph(32.19 km/hr) and 35mph(56.3km/hr).2 Since the moped will need to go faster than this at times, we’ll take the maximum speed to be 70km/hr and the optimal speed to be 40km/hr. Basing the estimation on the Smart Scooter XM-5000Li from Wholesale Motorsports, the weight of a scooter is 363lbs (165kg) and the maximum rider weight is 400lbs (181.8kg).3 This means that two people of around 200lbs could ride comfortably. For this project, the weight of the scooter will be 150kg for easiness of calculations. Furthermore, the maximum allowable weight will be 200kg. With a safety factor of 1.5, which is appropriate for this application, the total weight that the engine will need to be able to power is 450kg. It will also need to be able to run at a maximum speed of 70km/hr.

Based on this, how would you guys recommend me proceeding to design the engine? Do I start with the links? From your perspective, what's the best link shape for this?
What type of space constraints am I looking at for this type of application?

Any input would be greatly appreciated.
Thanks
 
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  • #2
To estimate the power you need, look http://hpwizard.com/car-performance.html" .

Once you know the engine power you want, these are the basic equations for the engine (all in http://en.wikipedia.org/wiki/Unit_conversion" ):

Qm = P / bmep

Ab = spc X Qm / VE / MPS

S = Veng / Ab

D² = Ab / N / 0.7854

w = 3.14159 X MPS / S

T = P / w

Where:

Qm = volumetric flow rate (m³/s)
P = crankshaft power (W)
bmep = brake mean effective pressure differential (Pa) (2-stroke: 8.8-9.6 bar; 4-stroke: 10-11 bar; you should use the lower values for a typical moped engine)
Ab = total bore area (m²)
spc = # of stroke per cycle (2-stroke: 2; 4-stroke: 4)
VE = volumetric efficiency (no tuning: 2-stroke: 0.55; 4-stroke: 0.75-0.80) (int & exh tuned (2- & 4-stroke): 0.90-0.95)
MPS = mean piston speed (m/s) (typical moped engines are around 7 m/s, but this can be easily doubled if a faster revving (smaller) engine is needed)
S = engine stroke (m)
Veng = engine displacement (m³)
D = cylinder bore (m)
N = # of cylinders
w = engine angular velocity (rad/s)
T = engine torque (N.m)

The bore-to-stroke ratio (D/S) is usually between 1.0 and 1.3.
 
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  • #3
These are great links, tools, and equations you gave me here. Thanks a lot. I will start on these and let you know what I come up with.
Any more input is always welcome.
Thanks again for such an awesome post.
 

Related to Designing a single cylinfer 4 stroke engine for a moped

1. How does a single cylinder 4 stroke engine work?

A single cylinder 4 stroke engine works by completing four distinct processes - intake, compression, power, and exhaust. In the intake stroke, the piston moves down, allowing a mixture of air and fuel to enter the cylinder. In the compression stroke, the piston moves back up, compressing the air-fuel mixture. The power stroke occurs when the spark plug ignites the compressed mixture, causing a controlled explosion that pushes the piston down and creates power. Finally, in the exhaust stroke, the piston moves back up, pushing out the spent gases through the exhaust valve.

2. What are the key design considerations for a single cylinder 4 stroke engine for a moped?

The key design considerations for a single cylinder 4 stroke engine for a moped include the size and weight of the engine, the power output and torque, the fuel efficiency, the cooling system, and the cost of production. The engine must also be designed to fit within the frame of the moped and be able to withstand the demands of daily use.

3. How is fuel efficiency achieved in a single cylinder 4 stroke engine for a moped?

Fuel efficiency in a single cylinder 4 stroke engine for a moped is achieved through various design features, such as a small displacement, high compression ratio, and efficient combustion chamber design. The use of lightweight materials, such as aluminum, can also improve fuel efficiency. Additionally, incorporating technologies like electronic fuel injection and variable valve timing can optimize fuel consumption.

4. What are the advantages of a single cylinder 4 stroke engine for a moped?

The advantages of a single cylinder 4 stroke engine for a moped include its simplicity, compact size, and low cost of production. It also offers good fuel efficiency and can provide enough power for the lightweight and low-speed demands of a moped. The single cylinder design also allows for easier maintenance and repair compared to multi-cylinder engines.

5. What are the potential challenges in designing a single cylinder 4 stroke engine for a moped?

One potential challenge in designing a single cylinder 4 stroke engine for a moped is balancing the need for power and torque with fuel efficiency. The engine must also be designed to withstand the vibrations and stresses of daily use. Another challenge may be meeting emission regulations and noise restrictions. The overall cost of production and the availability of suitable materials and components can also pose challenges for engine designers.

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