For some Americans, the thought of a diesel engine conjures up images of noisy, lumbering tractor-trailors belching clouds of black smoke. While that may have been an accurate depiction 20 years ago, it’s not anymore. Today’s diesels are clean, quiet, powerful and efficient. In fact, they’re cleaner and more efficient than gasoline engines, causing consumers to take notice. Last year, U.S. sales of diesel-powered passenger vehicles increased 27%. This while overall sales were up just 10%, hybrid market share declined, and electric vehicle revenue fell short of projections. Continue reading
These days, multi-million mile commercial vehicles are no longer the exception to the rule. They are the rule, making engine durability even more important. One key component of durability—managing cylinder thermal loads—is a known engineering challenge for conventional engines. And, that challenge is even greater for an opposed-piston, two-stroke (OP2S) engine. Unlike four-stroke architectures, the OP2S needs efficient cooling at the center of the cylinder where the heat load is highly concentrated. However, the two-stroke engine’s double-firing frequency makes this difficult—since the cylinder liner does not benefit from the cooling effects of the four-stroke engine’s separate intake and exhaust cycles. Continue reading
While there are many factors that contribute to an engine’s efficiency, the primary factor that needs to be considered is the engine geometry itself. Not only does the overall size of the engine matter, but the aspect ratio of the engine cylinders—defined by the stroke-to-bore ratio—also matters. To explain why, one must consider three factors: in-cylinder heat transfer, cylinder scavenging and friction.
Simple geometric relationships show that an engine cylinder with longer stroke-to-bore ratio will have a smaller surface area exposed to the combustion chamber gasses compared to a cylinder with shorter stroke-to-bore ratio. The smaller area leads directly to reduced in-cylinder heat transfer, increased energy transfer to the crankshaft and, therefore, higher efficiency. Continue reading
The first 200 seconds count when starting an engine. That’s because for many applications, more than 50% of the tailpipe emissions in an FTP-75 are produced in the first 200 seconds of operation after a cold start.
To help meet global regulatory standards and reduce cold-start emissions, Achates Power has developed a patent-pending temperature control strategy for achieving higher exhaust temperatures during the catalyst light-off phase than are possible with conventional, four-stroke diesel engines. Continue reading
Historically, opposed-piston, two-stroke (OP2S) engines have set combined records for fuel efficiency and power density. But, because they are piston ported, the engines were mistakenly dismissed for use in emissions-compliant, on-highway vehicle applications due, in part, to oil control concerns.
In 1998, however, Achates Power founder Dr. James Lemke began investigating the opposed-piston engine—seeking to prove that the architecture was not only fuel efficient, but could also overcome the inherent challenges with oil consumption and emissions. Continue reading
I’ve started a number of companies in my career, in several different industries. While I took my Ph.D. in theoretical physics, I’m a pretty applied guy—I tend to look for new ways to solve problems. In addition to being a physicist, I’m also a private pilot with more than 7,000 hours of flying time. I’ve flown a number of different planes over the years. A multi-engine plane, of course, has the advantage of allowing a pilot to continue flying if one engine fails, but the vast majority of private pilots fly single-engine planes. I began to wonder if there was a way to design an engine that is both light and fuel efficient so that two could be ganged together to drive a single prop, Continue reading
Medium- and heavy-duty vehicles use 26% of all U.S. transportation liquid fuels. That’s expected to increase at least until 2035, according to the Department of Energy (DOE) and the Energy Information Administration (EIA). Also of concern are the greenhouse gases emitted by these trucks, begging the question: what can we do about it?
In 2008, I was asked, along with 18 other committee members from academia and industry, to participate in a study on how to improve fuel economy in medium- and heavy-duty vehicles. Continue reading
Heavy-duty trucks are the fastest growing contributors to greenhouse gas (GHG) emissions within the
transportation sector, producing nearly 20 percent of GHG and accounting for 17 percent of transportation oil consumption. Because of this, the U.S. Energy Independence and Security Act (EISA) of 2007 directed the National Highway Traffic Safety Administration (NHTSA), in consultation with the Department of Energy (DOE) and the Environmental Protection Agency (EPA), to study the fuel efficiency of heavy-duty trucks and to implement, for the first time ever, fuel-efficiency standards for these vehicles. Continue reading
There has been a tremendous change in the energy outlook of the United States in just the last few years. U.S. dependence on foreign oil peaked in 2005 and declined dramatically since then, according to the Energy Information Administration. In fact, last year U.S. dependence on foreign oil fell below 50 percent for the first time since 1997. The reason: domestic demand is down and domestic supply is up. Continue reading
Opposed-piston engines (OPEs) have been around a long time—more than a century to be exact. First manufactured in 1890, these engines continue to be used in ground, marine and aviation applications worldwide. Unlike traditional four-stroke engines, OPEs combine two pistons per cylinder, working in opposite, reciprocating motion. This eliminates the cylinder head and valvetrain—considered among the most complex and costly components in conventional engines and the primary contributors to heat and friction losses. Continue reading