Thursday, December 27, 2012

A Long Overdue Update! The engine runs!

The engine is finally in an operational state, and doing very well. When did this happen? Well...

School and life have recently distracted me from my efforts to share my projects, but work on the gas turbine has continued.

I haven't been documenting the progress as closely as in earlier posts, so I'll do my best to pick up where I left off.

To start with, the evap system is finished. Here are some pics of the completed assembly:

The flame tube, also known as a combustor liner (the long tube within the combustor, which fits over the top ~3/4" of the evaporator plenum) has also been completed. This element serves a simple, yet crucial purpose. It allows for a uniform flow of air into the plume of burning fuel. This stabilizes the flamefront (prevents inlet air from "blowing out" the flame in the combustor), and controlls the heating of the air moving through.

Many belive that these engines run only by virtue of the expanding gasses resulting from combustion.

In fact, only a small percentage of the air moving through the engine is used to burn fuel. The majority of the air is simply a working fluid, which is heated by the combustion process at a constant pressure, and increases in volume (which translates in an increase in velocity, and inertia)

If you don't belive me, take a look at the T98-NT-XX gas turbine built by the guys at Nye Thermocynamics Corp.

Its a gas turbine which runs on wood!

The holes are all of a very specific placement and diameter, in order to provide the optimal mixing flow speed through each section. The holes on botom (towards the front end of the combustor) compose the primary mixing section. These small holes minimize turbulent flow of air into the flame tube, while maximizing the volume of air flowing, in order to burn all of the fuel spilling out of the evaporator. The medium-sized holes in the middle of the tube comprise the secondary mixing section. These are of a larger size, and total flow area, in order to provide a moderately turbulent flame/air mixing zone. This supports more complete combustion, and heating of the air flowing through. The tertiary zone (the large holes towards the top) provide a path for the rest of the air moving through the combustor to cool combustion gasses, and enter the turbine.

The last major component I've completed is the jet nozzle.

This nozzle gradually reduces the turbine outlet diameter from 5" to 3", inducing an increase in exhaust gas velocity, for the same mass flow leaving the exhaust.

The engine is running, but what good is that? Keep posted for more developments!

Wednesday, January 25, 2012

Evap System Nears Completion

Work on the evap "can" continues nicely, although with the hickups of a broken mill and a short lack of welding gas. I've also invested in a new Horizontal Bandsaw! It has already proven it's worth, and I'm very happy with what it allows me to do.

Since, the mill has been fixed and gas has been gotten. Now its time to proceede with the construction of the evap system. I cut off a 3" section of 4" diameter stainless tubing from the excess on the end of the combustor, then cut , pinched, welded, and ground the piece untill it fit snugly inside the 4" flametube. I then welded it to the evap "can" base.

Folowing this, I drilled a 1" hole in the center of the "twin" plate to the one that is the base of the evap can. I cut another 2" circle as the base of the evap tree, and proceeded to drill 3 holes which will hold the evap "tree" onto the "can".  I then drilled a large 1" hole in the mount for the "tree".

To make the tree, I used a hole-saw to profile the ends of three 3/4" tubes (the branches) to fit a 1" main "trunk", then cut each "branch" at 45* so they would make a nice "J" turn twoards the front of the combustor.

I'm using two different fuel injectors for two different fuels. The first and foremost is the main fuel injector. This is a cone-pattern spray nozzle that will evenly cover the sides of the evap tubes with a spray of diesel to be vaporized and burnt during normal operation.
The second injector is for the propane starting fuel. The evaporative fuel system can't be used unless the evap tubes are hot eanough to vaporize liquid fuel. To heat them up for starting, I'll use a small propane "pilot" injector. This is just a standard brass hex-plug you'd find in the plumbing isle, into the sides of which I've drilled some small holes. The radial hole pattern will be better for heating than injecting propane straight down the length of the combustor.

More to come soon!