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The Achates Power Engine: Low NOx and Superior Efficiency

Diesel engines have many virtues, including excellent fuel economy, great low-end torque and superior durability. They tend, though, to be more expensive than gasoline engines. One reason: for cars and trucks to meet global emissions standards, diesel engines need expensive aftertreatment equipment. The two most problematic diesel engine pollutants are NOx and particulate matter (PM). NOx—the general name for nitric oxide (NO) and nitrogen dioxide (NO2)—and PM have a somewhat inverse relationship. With low combustion temperatures, PM is higher and NOx is lower. With high combustion temperatures, NOx is higher and PM is lower.
 
Diesel engine manufacturers have several ways to reduce NOx emissions. Continue reading

Opposed-Piston Engines with Variable Compression Ratio

Opposed-piston engines (OPEs) have been around since 1858 and serious variable compression ratio (VCR) devices have been available since the early 1950s. Most applications were primarily research endeavors, with the goal of creating mechanisms that can achieve the benefits of VCR reliably, durably and for reasonably low cost.
 
Before exploring previous OPEs that have experimented with VCR, it is perhaps appropriate to examine the variable compression ratio benefits that have already been identified and achieved. Continue reading

Turbocharger Efficiency: An Underappreciated OP2S Advantage

There are a number of factors that contribute to the inherent thermal efficiency of the opposed-piston engine. Often, however, turbocharger efficiency is an overlooked and underappreciated advantage of opposed-piston, two-stroke engines (OP2S) like ours. Due to the two-stroke cycle, the OP2S has a natural fit to the high efficiency points of a turbocharger’s compressor map.
 
Turbochargers are used in all clean diesel engines—and, increasingly, in gasoline engines—to improve engine performance and powertrain efficiency. Continue reading

The Latest from SIAT

This week, I am pleased to attend the bi-annual Symposium on International Automotive Technology (SIAT) in Pune, India, where I will present a paper: Modernizing the Opposed-Piston, Two-Stroke Engine for Clean, Efficient Transportation. India, of course, is the second most populous country in the world and its economy is one of the fastest growing. At the Inaugural Function of the Symposium, Member of Parliament Supriya Sule noted that the transportation sector is growing more quickly than other industries, while also highlighting how the perception of diesel engines has changed from dirty to clean and efficient. In addition, Mrs. Sule identified one of the important challenges to the sector—the need to reduce vehicle emissions. Continue reading

Developing the Next-Generation Combat Engine

Improved fuel economy is important for many applications, but it is especially important for military vehicles. These vehicles are adding armor to protect against improvised explosive devices. They’re also adding expensive and heavy armament and communication technology. As the vehicle weight increases, so does the need for more powerful engines to maintain the same performance characteristics. And, these more powerful engines add weight.
 
One way to reduce this weight, however, is to use propulsion systems with high power density. A paper written by Charles Raffa, Ernest Schwarz and John Tasdemir of the U.S. Army Tank Automotive Research, Development and Engineering Center (TARDEC) emphasized that the “real need is for the complete propulsion system to be power dense”. This includes the engine, transmission, cooling system, air filtration system, intake and exhaust ducting, controls, accessories, batteries, fuel systems and final drives. A key way to increase the power density of the propulsion system: use a more efficient engine, since it can dramatically reduce the volume and weight of the fuel required for a given range. Continue reading

The Emissions Challenge

In 1970, the U.S. passed the Clean Air Act, putting limits on the emissions produced by motor vehicles. Since then, emissions regulations have become even more stringent, with modifications made in 1977 and again in 1990. Nearly every country in the world has implemented similar increasingly stringent emissions standards. In response, automotive manufacturers have developed innovative new technologies (such as improved engine performance and exhaust aftertreatment) and systems (including on-board vapor recovery and on-board diagnostics) to meet the latest regulations. The result: a nearly 99% reduction in criteria pollutants—which include carbon monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2) and particulate matter (PM).
 
While a 99% reduction is an impressive accomplishment, the regulations and associated technical improvements that have been implemented don’t address carbon dioxide (CO2) emissions in any meaningful way. Continue reading

Heat Transfer Advantage of Opposed-Piston Engines

To maximize the efficiency of an engine, one must minimize losses. Heat transfer to the cylinder and piston walls is a large source of heat loss in engines. Cooling systems keep these engine components from overheating, but all that heat being carried away by the cooling system is lost energy.
 
Many factors contribute to the heat transfer—and energy loss—of an engine, but a major one is the ratio of the surface area of the combustion chamber to the volume of the combustion chamber during combustion. The higher the ratio, the greater the heat loss as there is more surface area to absorb the heat from combustion. Continue reading

Just Back from the MTZ Heavy-Duty Engines Conference

ATZ Live—part of the publishing group behind MTZ and other technical magazines—organized a conference in Nuremberg, Germany last week with a focus on heavy-duty, on- and off-highway engines. I had the chance to attend this conference and also delivered a talk introducing our latest, exciting results.
 
The conference is an annual event and this year was the seventh time engineers from the heavy-duty engine industry got together. Over the years, the conference moved to the locations of the heavy-duty engine manufacturers. This year it was held in Nuremberg, which is the home of MAN. Continue reading

Greetings from Beijing

This week, I attended CALSTART’s U.S.-China Clean Truck and Bus Summit in Beijing. The event brought together representatives from key agencies of both countries with the goal of increasing U.S. exports of clean transportation technology for trucks and buses.
 
While at the conference, I participated in a panel titled “Spotlight on U.S. Industry Leaders”, along with Shiyi Zhou of Eaton and Ning Lei of Navistar. And, over the course of the three-day event, I made the following observations: Continue reading

In What Way Is a Hamburger Like a Truck?

California has been leading the effort for ever-lower vehicle emissions standards for decades, largely due to smog problems in the Los Angeles basin. A unique confluence of factors makes L.A. particularly susceptible to smog. The eastern edge of the basin is ridged by the Transverse mountain ranges, which often cause temperature inversion layers that trap exhaust. Combine that with a dense population, a heavy reliance on automobiles, and a large port and you have a recipe for smog. And since L.A. gets essentially no rain from May to October, there is nothing to provide relief.
 
As a southern California resident, I am glad that the significantly reduced emissions from cars and trucks—driven by standards from the California Air Resources Board (CARB) and the U.S. Environmental Protection Agency (EPA)—has literally cleared the air. Continue reading