Our first block has been poured at the foundry – ACTech in Freiberg, Germany. I was tempted to title this post as, “It LIVES!” We have been working on computer models of this complicated part for so long, to finally see a photograph of a real block made of compacted graphite iron instead of 1’s and 0’s is very very exciting.
MkII Clarke-Brayton Engine block just after being poured at the foundry
The block is now being prepared for machining, after which it will look much sleeker! The bulk of our smaller parts are already out for quote and we anticipate beginning testing on August 1st. Maybe I will save the, “It LIVES!” post title for when the engine is actually breathing.
Happy Memorial Day, everybody!
I have been woefully absent from these pages the last several months since we started the design effort on the new engine. I am excited to finally be able to share what the team has been working on so dilligently. The MkII Clarke-Brayton Engine is the next step in dramatically reducing fuel consumption in trucks, automobiles and generators without increasing costs. It is also the next step in developing a highly efficient compression-ignition 100% natural gas engine that can meet the up-coming greenhouse gas emissions regulations. This is a boxer configuration split-cycle engine implementing what we have come to call the Clarke-Brayton cycle. The thermodynamics of this engine are virtually identical to our previous “CCI” design but are implemented in a much more conventional way. Everything that we published in our SAE paper at the 2013 World Congress holds true for this engine, but many of the difficulties related to the old engine are resolved.
MkII Clarke-Brayton Engine
Section of the MkII engine
As with the previous design, in the MkII air moves sequentially through three cylinders, starting at the mid-sized cylinders at the top of the section image. This architecture allows us to achieve a 56:1 compression ratio leading to a 30MPa peak pressure. It has far less surface area for heat loss than a comparable conventional diesel due to the very small bore of the combustion chamber. The small combustion piston area leads to lower forces on the crank than a conventional engine would have if it were able to reach similar pressures, reducing rod bearing friction compared to conventional architectures. A lack of net forces on the main bearings due to the opposing forces of the piston pairs reduces main bearing friction compared to conventional engines. It expands exhaust gasses all the way to ambient pressure before the exhaust stroke. Gas transfer from one cylinder to the next is begun at equal pressures on either side of the valve, which keeps velocities low, minimizing pumping losses and eliminates blow-down. The power is produced in almost a 50-50 split between the combustion (central) and exhaust (largest) pistons. There is a power stroke every revolution. All valves are actuated by overhead cams. Piston ring sealing is completely conventional, eliminating the dynamic effects of the old design and greatly reducing the reciprocating mass.
The major components of the MkII Clarke-Brayton Engine have already been released to the foundry for casting and everything else should be released for fabrication within a couple of weeks. We will test this summer at a globally renowned engine development lab and I hope to have results to share shortly after that.
A team of just three people designed the MkII from a back-of-the-napkin idea to a fully developed test engine in 7 months. Azra Horowitz and John Clarke have both put in herculean efforts to get this done in time despite a couple unexpected thorny technical challenges along the way. I could not be more proud to be working with them.
We do not focus much on PR around here (yet), but an article was just published in Babson Magazine that features us called, “Risky Business with a Purpose”. It was a real pleasure speaking with Donna about Motiv and kinda fun doing the photo shoot out in Brooklyn with people stopping and staring wondering if I’m someone famous. Sorry for the disappointment, people!
Kickoff day for the design of MkII of our engine is coming soon – September 23rd. Our two new engineers, Azra from MIT and Abhishek from Stanford, will be starting that day and John will be in town for the week. I’m busily getting the new office ready. As you can see, it is still mostly empty. It’s 1350 square feet in Midtown South in Manhattan on West 36th Street. I will post pictures of it once it is done. Furniture is being delivered tomorrow. I have the new Dell M4700 mobile workstations and 23″ monitors as well as a new PowerEdge server. Our design software should be here tomorrow. Here is a before picture. I’ll post more pictures once everything is all set up.
Our new, empty office
Somehow popular lore makes it seem like orientation for a startup should be full of games, lavish parties and tons of promotional gear with quirky logos. Ours will be a little bit more like jumping into the middle of an advanced graduate thermo-sciences semester… But for us that is actually fun! I can’t wait until we finish the first part kick-off meetings so I can watch how the engine is born and see what it looks like, part-by-part. I considered having the first orientation task for the engineers be unpacking and assembling their desk and chair, but that does not seem very welcoming, so hopefully I will have all that done before they arrive!
Some big things are happening at Motiv Engines! As the title says, we have a new team of engineers, a new office in Midtown Manhattan, and a new engine design. I will introduce the engineers to you soon. The engine itself may take a while before I can give details, but I can provide some key ideas behind it. We get possession of the office on September 1, and I’ll give a little online tour of it after it is up and running.
With our first prototype we did not run into any thermodynamic surprises, but we did have some issues related to the mechanism. There are several things that we are doing mechanically different than the norm, and some of these things proved tricky. When we modified our thermodynamic simulation to include the mechanical things that were going wrong, the results perfectly matched our experimental data. This gave us even more confidence that our theory is strong, but the mechanical implementation was lacking. So now we have a new design that addresses all of those issues. It should be vastly simpler to build, assemble and maintain, and believe it or not, it will be even smaller. Thermodynamically it is exactly the same.
In mid-September the new team will begin detailed design of the new engine. We hope to have the new engine in a test cell having produced data in less than a year. It is a very exciting time!
Last week we were in Detroit and John made the first public presentation on the CCI engine at the SAE World Congress. He did an excellent job and I feel that even though I am biased, it was one of the best presentations in the session. The other notably good presentation of the session was by Mahle on piston ring pack design.
John Clarke presenting the CCI engine at SAE World Congress
After the presentation, we were at a table in the lobby working on a slide deck for a meeting the next day when we were approached by a group of Stanford students that had seen our presentation. They had some very insightful questions and there was a lot of mutual respect shown between John and the students. I give you this exchange that I found to be particularly entertaining:
John: I love Stanford students because they actually know thermodynamics.
Stanford Student: Oh gosh, thanks! I was just so glad to hear a presenter who actually knows what exergy is!
SAE, we look forward to coming back next year and presenting the progress we’ll make over the coming year!
John has been in Detroit throughout the weekend attending the High Efficiency IC Engine Symposium and I am arriving today to join him for the World Congress. John will be presenting our paper on the CCI Engine:
The presentation is Wednesday, April 17th, at 2:20pm in room W2-68. Here is a link to our session schedule. I hope to see many of you there!
On November 13th, the EIA forecast that the US would become a net exporter of natural gas by 2022 as reported by Reuters. The US is using more natural gas for power production, and even transportation fuel, as the recently reported T. Boone Pickens Clean Energy Fuels Corp. deal with GE highlights. All of this is happening even though there are a number of drawbacks for natural gas engine fuel storage systems because the economic, geopolitical and environmental benefits to doing it are so strong. This gives some certainty that natural gas will play a major roll in the portfolio of future North American energy resources. I find this all to be very positive not only for our country, but for the CCI Engine.
I have written before about the benefits of the CCI running on natural gas. Its ability to use high compression ratios and direct injection without requiring a pilot injection of diesel or some other ignition aid makes the efficiency and cost of the CCI leaps and bounds ahead of other solutions such as the Cummins Westport engines. There are even possibilities that the CCI could use natural gas as a Homogeneous Charge Compression Ignition (HCCI) fuel for a really low-cost low-emissions natural gas engine.
I think the move to natural gas makes the already attractive CCI engine even more attractive. It’s benefits in efficiency and power density hold just as true for natural gas as they do for diesel or biofuels. With natural gas we have an added benefit over current technology in that just getting close to diesel-like efficiency with NG today requires very expensive engines and dual fuel. The CCI can exceed that efficiency level with a reasonably priced engine and a single-fuel system.
A couple of weeks ago, we began testing with our new pistons, rings and low-pressure seals in the ground-breaking CCI engine which promises to be the most efficient engine in the world. I am very happy to report that the engine fired! This is a huge milestone for us and is another step in demonstrating to the world that this engine is not just theory, it is real.
The engine also reminded us that this is ground-breaking work and every step forward comes with new challenges. Whether it was from the increased stress on components from the pressure of firing, or just collective time, some washers under bolt heads bent, causing a chain reaction of mis-alignments that cracked a component that then caused leaks, necessitating a small re-design and re-manufacturing of the component. The causal problem has been addressed and we should be back on the test cell soon.
The CCI Engine has a thermal efficiency of 52%, is 1/4 the size of a conventional diesel engine of the same power, and can burn natural gas as a direct-injection, high-compression fuel without the use of other fuels as pilots or spark plugs.
So we have completed our new high-pressure piston design and it is out for quotes. In our last re-design effort we tried modifying our existing pistons rather than starting to start from scratch in order to save money. This led us to try some “innovative” ring designs to make it work. Turns out there is a reason engine rings and grooves are made the way they are. Who knew? So this time we’re making all new crowns using current best practices – or at least as close as we can get to it. I won’t go into exactly what we’re doing and why, but I’m excited to see how these babies perform. I wanted to put in a picture, but I’m worried that perhaps there’s something in there we will want to patent so no graphics for you today.
When assembling the engine, getting the cranks in sync and controlling gear lash has been a labor-intensive effort that is very easy to mess up. To alleviate this we have designed a new doohickey (that’s a technical term) that lets us do this in a much more controlled and repeatable manner, eliminating another unknown source of potential error for us. Finally, we’ve got some new seals for our low-pressure pistons which should be another enhancement, but without as dramatic improvements as our new HP pistons. Our new shaft syncing device should improve the LP seals as well.
We’re adding some data channels to our test cell that will give us more insight into the performance of our poppet valves. Our pressure traces from our last tests tell us the timing is not what it is supposed to be, though at our low testing speeds, the effect on engine performance due to this error should be pretty minimal. The new data will allow us to ensure we get it right next time.