In my last post, I gave a brief explanation of how rotary engines operate. As mentioned, they still use air, fuel and spark to operate but they work with a higher compression than piston engines.

There are five parts to the engine design:  rear side housing, rear rotor housing, intermediate housing, front rotor housing and front side housing. An eccentric shaft runs through the center of all these components and this is what the rotors spin around. Each rotor is equal to three cylinders. The advantage these engines have over piston engines is that they have three sides to a rotor, and one chamber to spin so intake, compression/ignition and exhaust all happen at the same time on one rotor. As well, these engines have fewer parts than a piston engine.

The main disadvantage to this type of engine is that the seals play a huge role in how they operate and perform. The apex seal is like a ring on a piston. It holds the compression and scrapes the oil off the wall of the cylinder. The apex seals have to keep the compression (over 300 psi) and keep lubricated, or else the engine will not run. Oil is injected into the chambers to keep the rotor well lubricated and keep compression high.

A very important tip when driving cars that use a rotary engine is to get into a habit of revving them up then turning the key off and let them die out. This shuts off the fuel but injects oil into the engine. Without doing this, you could flood out the engine, washing away all the oil and loosening compression.

I have learned a lot about rotary engines, and I find them very cool and neat to work with. The video below is of an RX-8 that had a flooded engine and wouldn’t start. My work uses a special method to regain compression in the engine so they will run again. It’s really cool but they sure smoke when they fire up.

http://www.youtube.com/watch?v=0GUSk3vVwAA

A rotary engine is another type of combustion engine used to power a vehicle. It has similar principles to a regular piston engine, but is very different in design. In a piston engine, the piston goes up and down inside a cylinder. The valves open and close at certain times to allow air and fuel in, and exhaust gases out. A connecting rod attached to the crankshaft converts up and down motion to a rotational motion.

Rotary engines have a triangular shaped rotor that is attached to the crank and rotates inside the housing. These engines are complex in design and operate similar to a two-stroke engine. There is no valve train. The rotary opens and closes intake and exhaust ports as it spins around. These engines are smaller and compact in size, but are capable of putting out just as much power as a regular piston engine. They are capable of putting out very high RPMs and are found in Mazda’s production line of the RX-7s and RX-8s.

Our first step in repairing cavitation is to set up our equipment and begin using the plasma cutter to gouge it out. To do this you simply hold the torch at an angle and wash out the porous parts of the steel. You can see the cavitation disappearing as you get deeper into the steel.

When two welders are working together on a unit, one begins by gouging on one blade and when they move on to the next blade the other welder may bring in the welder and begin filling in the locations that were gouged. For this unit, we used a wire feeder with stainless wire. We use stainless wire when repairing cavitation because it withstands cavitation much better than steel. Even though this unit is not made of stainless steel we still use stainless to repair it. The welding is done by layering welds; and the goal is the make the weld as flush as possible to the contour of the liner or blade. When welding, the most difficult part I found is the first and last bead as most likely they will be made where a small portion of cavitation still remains. This makes the weld not to fuse very well to the material; it welds as though your voltage is too high or as if you don’t have any shielding gas, which is not the case at all. I found the best way to solve this problem is to make those bead in short sections, and as quickly as possible. Depending on the extent of the cavitation you’re trying to weld over, you will most likely have to go back to touch up, or use a series of tacks to fix any problems areas.

As you can see, extensive equipment is used when doing cavitation. A respirator is a must; I have a Speedglass respirator helmet. It is perfect for welding in any location because it does not have to be connected. There’s a battery pack and filter you wear around your waist. It filters the air and circulates cool air into your welding helmet. We also must wear leathers as the equipment we use gives off extreme heat and sparks. A white hood must be warn underneath our welding helmets as the arc rays can cause severe burns to the skin, which becomes worse when it is reflected off of the steel liner. Hearing protection is also necessary.

When any work is performed inside the draft tube, you must not be alone. If you are the only welder working on a unit there must be someone standing by as a safety watch.

We usually work 12-hour days gouging and welding, then a night shift comes in to grind down our welds flush. The finished product is what you see above.

Unit 4 is the only unit that was replaced with the new stainless steel runners, as I have explained in an earlier blog. Cast iron is more prone to cavitation than stainless steel is, due to its mechanical properties. This means there was a lot of cavitation that needed to be repaired.

Our first step was to crane down all of our supplies, including our job box, welders and our plasma cutter.

Scaffolding was already in place ready for us to move in lighting and begin mapping out the runner and liner for cavitation.

Prior to mapping out the runner we needed to have the turbine blades completely open. As a safety precaution, steel wedges were welded in place to prevent the turbine blades from creeping closed while we were working on them.

Due to the extensive damage cavitation caused on this unit, an engineer came to use dye penetrant to check for cracking on the turbine blades and on the liner.

After the dye pentrant was complete with no signs of cracking, we began repairing the cavitation

These are examples of extensive cavitation

It’s been 10 weeks and I have successfully completed my level two schools. Time for a quick vacation, and it’s off to Grand Rapids for my generation rotation. Talk to you soon!