Dear,
Since you are belonging the the mechanical engineering which is the hub for giving the real set examples in day to day techniques. The most famous and intrested topics can be
High speed trains
Rocket propellent
Turbofan engine
Air cars
A .c s
Solid waste management
Solar powered airplane
Airless tyres
Mechanical energy storage

Hello.
Here is the list of some of the popular topics for seminar in mechanical engineering:

• Hydrogen wire car.
  
• Air car.
  
• High  speed trains.
  
• Stealth  fighter.
  
• Turbofan engine.
  
• Pistonless  pump for rocket.
  
• Green  manufacturing.
  
• Robot  welding.
  
• Hyper  transport.
  
• Micro turbine generator.
  
• Boiler  operations,etc.
  

Best  of luck.