Disadvantages of Loop and Cross flow scavenging
Loop and Cross flow scavenging are no more found in any of the modern engines. This is because of the problems attached with having fixed ports.
The main disadvantage of having these types of scavenging is that it couldn't clear off the cylinder of all combustion products.
Also, the time for scavenging is too less for the scavenging period only lasts till the time scavenging ports are closed.Efforts were made to eradicate this problem by providing high velocity air, but the steeply angled ports couldn't allow the smooth entry and exit of the air.
Many new designs were introduced to eradicate this problem but they all proved unreliable due to some or the other drawbacks. In the new design there were chances of the inlet fresh air to shortcut directly to the exhaust port. The situation used to worsen when the scavenge ports were blocked due to carbon build up.
One more disadvantage of a cross flow is that it needs a piston skirt to be fitted in order to prevent the air or exhaust gas to escape when the piston is at the top of the stroke. This increases the load on crosshead bearings and also increased the wear of the liner.
The fitting of both inlet and exhaust port in the cylinder liner made the design and construction complex and also made the lubrication difficult. This lead to a higher need for lubricating oil and also increase in temperature.
In the loop flow, low temperature inlet air and high temperature gas causes severe temperature differences which causes detrimental effects on the cylinder liner material.