Two Stroke Engines Flashcards
How many crankshaft revolutions occur during the intake, compression, power and exhaust phases?
One revolution
What is used for the intake phase on a two-stroke?
The crank case
What happens during the intake and compression phase?
- piston moves up
- afm is compressed
- low pressure is created below
- low pressure draws in new afm into crank case.
What happens during the ignition/power phase of a two-stroke?
- spark ignites afm
- exploding gases push down piston creating torque
What happens during the exhaust phase on a two-stroke?
- piston travels down revealing the exhaust port.
- burnt gases escape; this is known as “exhaust blowdown”.
What happens during the exhaust and fuel transfer phase on a two-stroke?
- the piston is moving downward revealing the fuel transfer port.
- Fresh AFM pushes through the transfer port.
- scavenging begins: fresh AFM pushes out remaining burnt gases.
What are the two types of scavenging designs on a two-stroke?
Cross flow and loop scavenge design
How does the cross flow design help with scavenging?
- piston dome helps direct the afm.
- piston tip has a special design that also directs afm.
What are some draw backs of a cross-flow design?
- at high rpm, some burnt gases get left behind.
- The piston tip gets very hot and causes irregular strokes.
What are some benefits of a loop scavenged design?
- multiple ports to direct afm and exhaust.
- better scavenging takes place
- better fuel economy.
How does a two-stroke get lubrication?
- An oil/gas mixture: 25:1 or 50:1
- some designs have an oil injection system that uses the crankshaft.
What are some advantages of a two-stroke?
- less parts = less to malfunction
- lighter
- can run in weird angles.
What are some disadvantages of a two-stroke?
- shorter life span: poor lubrication
- additional costs of oil
- noisier
- loss of fuel from scavenging
