Tech Briefs is the publishing arm of SAE international and publishes NASA Tech Briefs, Automotive Engineering and more. They are holding their annual Create the Future Design Contest and we have entered the Clarke-Brayton Engine! There’s a lot of competition on there, so we need your help! Please register and vote. I know registration is a pain, it will really help us out! Here’s the link:
After many months and modifications to get the engine running smoothly we are finally getting great data! Not only is the data itself high-quality but they are showing that the engine is performing excellently. I wish I could present the detailed data, but unfortunately it is still confidential, but here is a chart of pressure vs. crank angle of all three cylinders with the units removed from the axes:
Crank Angle vs. Pressure in the MkII Clarke-Brayton Engine. The circles and triangles are every 5th data point taken from running the engine. The solid lines are the predicted results from the computer simulation.
We’ve run the engine for up to 30 minutes continuously at full-power. We’ve learned that the engine is in fact extremely efficient, cooling the engine is not nearly as big of a challenge as we thought it might be and that we can improve even further on our current design.
Since the beginning of the MkII project in October 2013 we have spent just $800k covering ALL expenses. I’d like to see any other engine company be so cash-efficient! If we can accomplish this much with so few resources, just imagine what we will do when we raise significant funds and engage with world-class strategic partners.
Here’s a video from one of our longer-duration test runs.
My last post was about the machining of our “low pressure” pistons. Our combustion pistons start out with a very different kind of fabrication process: Direct Metal Laser Sintering (DMLS). It is a kind of 3D printing. Believe it or not, finding a short, entertaining video about DMLS is difficult. So instead please enjoy the least annoying video about the process I could find:
Here is what the parts look like just after printing.
This had to be printed because there are some internal cooling passages inside of them that traditional machining cannot make. In mass production this is handled by making them in two parts and then friction-welding the two halves together. For just two prototypes, that is not economical, thus we went with DMLS. There is still a lot of machining and grinding to do before the pistons are done. Eventually, they will look like this:
Edit: Here is a finished piston next to one of the blanks!
Finished piston next to printed blank.
Austin Jones at J.H. Benedict has been very nice to send us several pictures of our 4340 steel exhaust pistons throughout the manufacturing process. They are almost finished. There is still some grinding to do and some machining on the crown. You can see they did the turning operations first on the lathe, and then machined out the inside of the piston. Bushings for the wrist pin will be machined and ground out of a bronze alloy and pressed in later.
4340 steel billet for the piston beginning the process.
First turning operations for the piston are complete.
Machining processes on the piston.
Roughing out the inside of the piston on the mill.
The piston is nearing completion! Lands and grooves are still to be ground, and the crown is still to be machined. Bushings will be pressed in later.
I thought some people might get a kick out of seeing how the sand casting process that we used to make our blocks and crankcases works. It combines a bunch of different manufacturing techniques from rapidprototyping (commonly called “printing”), casting and machining. A mold into which the molten metal will be poured to make the engine block must be made. It has outer walls that define the shape of the outside of the block, and it has “cores” that define the shape of the internal cavities of the part. These are made out of sand that is held together with a binder material. The way these are made these days is to use a laser-sintering process. A computer-controlled laser hardens a thin layer of sand in the shape that is required for the core or mold part. Then a fresh layer of sand and binder is deposited onto the just-hardened layer and the laser makes another pass, building up the part layer-by-layer.
Sand cores for the MkII Clarke-Brayton engine
Above you can see a variety of the sand cores and molds that were used for our engine block/head. Basically, you need to have sand filling up all the spaces where you do not want metal. Building the mold is kinda like building a “negative” of the engine. All the cores are assembled together.
Special coatings are sprayed on to improve the surface finish of the metal and ensure that sand does not stick to it.
The cores you see assembled here will be passages within the engine block. Some of these passages will be to allow the air to flow through the engine as needed. Some will be for coolant to flow through making sure the engine does not get too hot.
There is a last piece that goes on top of the assembly you see above but unfortunately I do not have a picture of the whole mold ready for pouring. In designing the mold, special care needs to be taken that the molten metal will be able to fill up all the gaps completely, allowing air to escape through vents as more metal is poured in.
After the metal cools and hardens, all the sand gets broken up and cleared away, leaving just the metal part!
That part is closely inspected using 3D scanners to ensure dimensional tolerances were maintained and x-ray scanners to make sure there are no internal cracks or other problems that cannot be seen from the outside.
Next the part is put in to computer-controlled machining centers that will cut away excess material and provide all of the tightly controlled dimensions, surface textures and other features that are required to make an engine work property!
Here is a video that shows a similar process being done for a different engine block. This video was not made at the foundry that is casting our parts.
What an exciting week! I finally got the new office 90% ready and our new team showed up on Monday to begin work. The first thing to do is introduce our new engineers.
Seated around the conference table in the new office from left to right: Ed O’Malley, John Clarke, Azra Horowitz, Abhishek Sahasrabudhe
Abhishek Sahasrabudhe came to us after finishing his MS in Mechanical Engineering at Stanford. He has experience working on an advanced engine efficiency technology at Bosch Automotive. He was a graduate research assistant at Stanford where he was also a teaching assistant in the finite element analysis class. Abhishek completed his BS in Mechanical Engineering at the University of Pune in India where he graduated first in his class.
Azra Horowitz recently completed his BS in Mechanical Engineering and Physics at the Massachusetts Institute of Technology where he studied internal combustion engines under Dr. Wai K. Cheng. He has designed a novel organic rankine cycle engine for powering submersible unmanned autonomous vehicles and was the winner of the Sherman Math Prize at Wesleyan University.
I could not be more pleased with our team, their knowledge of engine thermodynamics and design, and their enthusiasm. It makes Motiv a very exciting place to be and we have already launched the design effort on the new engine. This work is being done in our new office, of course. Here are some more pictures, before we got started working in it.
Desks with Dell M4700 mobile workstations and 23″ second monitors.
Break area. Fridge and microwave to be added to the already well-used coffee maker!
We started the week out with a review of engine thermodynamics, as well as general engine design concepts implemented in applications ranging from model airplanes to Ferrari Formula 1 race cars. It was a great way to get the gears turning (pun?) and prepare our minds for the task ahead!