With efficiency being the bandwagon every automaker wants to hop onto, many new ideas are being pondered upon. These ideas aim at enhancing efficiency whilst maintaining cost-effectiveness. One such idea comes from Achates Power Inc, which has developed an improved version of the opposed piston two-stroke engine. Auto Tech Review spoke to Laurence J Fromm, Vice President, Business & Strategy Development, Achates Power Inc to understand how different and viable their solution is.
Laurence J Fromm joined Achates Power in 2004 as the market-facing executive of the company's founding team. In his present role, Fromm leads engagements with leading engine, commercial vehicle, and passenger vehicle manufacturers around the globe apart from managing the business development, government relations and marketing. Prior to Achates Power, Fromm served as the CEO of Chaos Telecom, a venture-backed early-stage company. Fromm is also a board member of NCast, Inc, a company developing a webcasting Internet appliance, as well as a steering committee member of CommNexus NextStage, a non-profit industry organisation that mentors early stage companies through an entrepreneur advisory programme. Fromm has a Bachelor of Science degree in computer engineering from the University of Michigan and a Master of Business Administration from Harvard Business School.
ATR _ Opposed piston engines have been around since many decades but have failed to become part of mass mobility. What encouraged Achates to take up this architecture?
Laurence J Fromm _ Opposed piston engines have a long history, going back to the 1930s and 1940s. They’ve always had an efficiency advantage over other comparable four-stroke engines. In such an engine, two facing pistons (opposed pistons) come together at top dead centre in a single cylinder and move outwards after combustion. As these pistons cyclically cover/expose the intake and exhaust ports, the need for a valvetrain is eliminated. This helps in saving weight and cost at the same time as the cylinder head is also done away with.
But with two pistons wouldn’t you need two crankshafts, thereby offsetting the cost-benefit somewhat?
Yes, we use two crankshafts connected to a gear train, which provides the ability to have the power taken off of any crankshaft or idler gear. The cost-benefit isn’t offset much and despite the addition of a second crankshaft our engine costs less.
Could you explain the basic architecture in brief?
A thought experiment here would be to imagine a six-cylinder inline engine, take out all cylinder heads and cut it in half. Now flip the right half on top of the left half and you have the opposed piston engine. Although it’s hard to explain in a few words but this engine features leaner and faster combustion, both of which aid efficiency.
Why couldn’t opposed piston engines find popularity then through these decades?
People stopped using this engine around the 1950s and 60s as countries around the globe started formulating emission standards – a practice nobody could afford to miss. In a two-stroke engine the gas exchange process is very complicated. Hence, companies stopped making these engines at that time and focussed on the relatively simpler four-stroke engines. The difference today is that efficiency is much more important. With extremely powerful computers and analytical tools we can solve the gas exchange problems and combustion problems analytically.
Is Achates Power the only company working on it right now?
The engine has historically been used for many applications and is still being used today in power generation and marine engines. The unique contribution from our end is that we’ve modernised the architecture and made it clean and efficient so that it can get back to the highway. We started working on this engine around 2004 and have made number of inventions since then. So, while there are people making opposed piston engines, they’re not clean enough to meet the emission standards and aren’t as efficient or durable as our engine.
Compared to a four-stroke engine, what are the gains in terms of efficiency?
It’s about 20 % more fuel-efficient and from the emission perspective there are mandates, and we meet all of them as required. There’s not much gain in going below the mandate as the costs would escalate significantly.
How different is the power density?
Power density is better because ours is a two-stroke engine, which means every cylinder fires in every revolution. One could replace a 6-7 l four-stroke truck engine with a 5 l engine from us, thereby extending the multiple benefits of smaller size and lesser weight. In fact, Achates and AVL just won a US Army contract to supply the next-generation combat engine. The three main criteria for selection were excellent power density, fuel-economy and low heat rejection to coolant. The low heat rejection to coolant also means the frontal area of the radiator for trucks can also be reduced, leading to enhanced aerodynamic efficiency. This would further increase the overall efficiency, a critical parameter for any CV operator.
What kind of trucks are we talking about?
I can’t talk of all such details but we’re working on different combinations and sizes. We’re also working with a partner for developing heavy-duty CV engines for Class 8 trucks. So our engine will act as a replacement for engines in the range of 13-15 l.
Any plans to enter the passenger vehicle segment?
Absolutely! Our engine’s advantage is that it’s efficient and costs less as there are no cylinder heads and valvetrain. It just so happens that trucks are a better initial market since they naturally consume lots of fuel. Hence any engine offering more efficiency will receive acceptance, which is the case with us. Acceptance for any new product is a challenge initially and the truck market is more open to accepting new technologies provided they are more efficient. In the car market, acceptance takes longer. Nonetheless, we see the passenger segment as our next target market as efficiency is one of our key USPs.
How does this engine fare in terms of NVH levels?
It performs at almost same levels as its competitors and meets all mandatory and customer benchmarks. Also, a three-cylinder engine of ours would typically replace an inline six-cylinder truck engine. Since the three cylinders are firing every cycle the firing timing is almost identical to the engine it replaces and hence the sound levels too would be almost same.
Since a fair part of the architecture of the opposed piston engine is similar to the four-stroke engine, how well does it respond to forced induction?
Our engine is turbocharged as well as supercharged. In a conventional engine, we ignite fuel when the cylinder pressure is high enough to create the required heat. In a two-stroke, however, we have to increase the pressure in the cylinder to start the cycle. So, a supercharger does this job and pumps air into the cylinder so that they can start firing from the beginning. We need the supercharger along with its associated recirculation valve to start the engine and adjust the boost pressure in the intake manifold to manage the gas exchange process, while minimising the pumping loss.
Since efficiency is one of the major highlights of this engine, what about the parasitic losses due to the supercharger and how different are they in comparison with the four-stroke engine?
Good question. It does have some parasitic loss and hence we first calculate all of that loss as the pumping work – the work done to get the air into and out of the cylinder. Four stroke engines have pumping work too. The levels of parasitic losses are about the same for both types of engines.
Engines of all kinds these days are employing some kind of exhaust gas recirculation (EGR) to meet NOx standards. Herein, the exhaust gas is pumped back into the cylinder and dilutes the fresh air, as a result of which temperatures are lower and so are the NOx levels. A two-stroke engine though is natural to this process and with a supercharger we can decide to only scavenge a part of the cylinder. At the end of combustion, instead of replacing all of the old air with fresh air, we can decide to push just some of the old air out. This in turn reduces our pumping work and that dilutes the charge naturally. This however, works at low-load operations and if the same were to be done during high-load operations, the temperature would get too high. Hence, over a full operating cycle our pumping work is about the same as a four-stroke or maybe a little less.
So the opposed piston engine doesn’t need an EGR?
We also have an external EGR that helps us maintain the natural cylinder temperature and control NOx.
How does the combination of turbocharger, supercharger and EGR then let you maintain a cost-benefit over four-stroke engines?
If you look at a conventional Euro VI or an EPA 2010 engine, you would find an EGR, cooler and a variable geometry turbocharger (VGT). The VGT apart from being used for many other things is also used for controlling the EGR. At high EGR levels, it will increase the back pressure by closing the vanes of the turbo in order to feed the air back into the cylinder. VGTs are very expensive; hence, we replace the VGT with a fixed geometry turbocharger (FGT). The cost of our supercharger and FGT is more or less the same or less than that of the VGT alone.
Any plans of moving to petrol engines? Also, where does India feature in your plans?
All of our work up till now has been done on diesel engine but we’ll look at petrol engines and natural gas as well, since it is a popular energy source in countries such as the US and India. Broadly, anything that is combustible can be worked upon and our engine will continue to offer higher efficiency with any of these resources.
Our goal is to work with companies making engines and get a small license fee for providing access to the technology. Since our engine costs less, despite counting in the royalties it would be less expensive for such companies in comparison with what they make today, but will have 20 % more efficiency.
India is an important market for any company today and so is it for us. We’re in initial stages of discussion with some Indian companies, which I cannot name right now. As of now we’re finding good interest from India in our technology and we look forward to exciting times in this market in the coming years.
At a time when the industry is shifting towards alternate mobility options, are you investing in technologies that might not be future-proof?
Not at all. First, our engine would be a nice compliment to a hybrid drive as it’s small, lightweight, low-cost and efficient. Humans are yet to invent a better way to store energy for transportation than liquid hydrocarbons. It’s dense, easy to ignite, store and transport. Hence for applications such as trucks and other heavy vehicles, liquid hydrocarbons will continue to be the fuel of choice. The idea of renewable hydrocarbons, however, is fairly attractive.
Text: Arpit Mahendra
Photo: Achates Power/ Arpit Mahendra