The American company Achates Power is now approaching vehicle OEMs across the world with a new engine that will cut down on fuel consumption and be more cost-efficient, says the company’s president. HUNED

CONTRACTOR writes…

In December 2015, The San Diegobased Achates Power announced that it received a contract from the US Department of Energy to develop a more efficient gasoline engine with initial funding of $9 million over three years. This as

been a tide of good fortune for a company that has invested more than a decade in developing engines that can improve fuel efficiency by more than 50 per cent compared to downsized, turbocharged direct injection gasoline

engines, while reducing the overall cost of the powertrain system. The company’s engines have opposed pistons. Two pistons share a cylinder, turning crankshafts at opposite ends of the cylinder. The company plans to build an

opposed-piston, gasoline compression ignition engine that will be two-stroke design with no spark plugs.

“The engine will dramatically reduce petroleum consumption and CO2 emissions, while meeting the current and future

mandates for low criteria emissions in cost-effective, high-volume products that consumers will love driving,” says David Johnson, CEO, Achates Power. The engine will be a three-cylinder, three-litre model suitable for large

passenger vehicles, pickup trucks, SUVs and mini vans. It would be possible to make two and four-cylinder engines of the same design. Elaborating on how the company has been engaged in revolutionising the engine

technology, Johnson, who has been a regular visitor to automotive exhibitions in India, explains, “With two pistons per cylinder, working in opposite reciprocating action, these engines do not need cylinder heads which are a major

contributor to heat losses in conventional engines. Ports in the cylinder walls replace the complex poppet valves and friction-creating valve trains of conventional engines. The intake ports at one end of the cylinder and exhaust ports

at the other are opened by the piston motion and enable efficient uniflow air scavenging.”

TWO-STROKE COMBUSTION CYCLE

A two-stroke engine produces twice as many power strokes per revolution as its four-stroke equivalent. This advantage leads to smaller displacement engines for similar performance, and lower in-cylinder pressure to lower

emissions compared to four-stroke conventional engines. In the past, these advantages were balanced by some well-documented shortcomings of two-stroke engines, which limited their scope of use. High hydrocarbon missions
(due to carburetion and over-scavenging) and excessive oil consumption (due to oilfuel mixing in spark-ignition engines and port oil ejection in compression ignition, direct fuel injection engines) are difficult issues to tackle in these

type of engines.

TWO-STROKE DIESEL ENGINE

The engineers and scientists started Achates Power in 2004 with the audacious idea that innovation and modern technology could transform the proven and record-setting two-stroke opposedpiston engines of the past into the

lean and efficient engines of the future. This advantage reduces the fuel used per cycle, resulting in shorter and leaner combustion for optimally phased energy release – all enhancing engine efficiency. “Our extensive prototyping

capabilities and state-ofthe- art test facilities are instrumental to confirm at every step the validity of our analytical approach and results,” Johnson states. The proprietary cylinder and piston designs achieve unprecedented

improvements in combustion efficiency and oil consumption to meet the most stringent emissions regulation. In conjunction with the thermal efficiency advantage inherent to opposed-piston engines, these designs realise signifi

cant reductions in fuel consumption over conventional four-stroke compression ignition engines.

When the cost of using fossil fuels becomes too high, improved compression ignition engines will be ready for the renewable fuels of tomorrow.” – David Johnson, CEO, Achates Power.

COMPRESSION IGNITION ENGINE

Compression ignition engines achieve superior thermal effi ciency by the virtue of their higher expansion ratio, inherent fuel-lean combustion and reduced pumping losses. Although the very first compression ignition engine,

designed by Rudolph Diesel in 1894, ran on pure peanut oil, today’s compression ignition engines rely on diesel fuel, thanks to its unique combination of qualities such as: a) energy dense, takes less volume and weight in

vehicles, b) clean, with the recent introduction of ultra-low sulphur diesel fuel, c) widely available throughout the world, d) most cost-effective in the current economic conditions. Compression ignition with diesel fuel is therefore the
combination of choice for the commercial transportation of goods and people on road, rail and water. 

In fact, in the US, 25 per cent of the fuel used by cars, trucks and buses is diesel fuel while in China and India, diesel represents

two-third of the fuel used for road transportation. “Improving further the effi ciency of compression ignition engines will reap huge environmental and economic benefi ts. And when the cost of using fossil fuels becomes too high,
improved compression ignition engines will be ready for the renewable fuels of tomorrow,” Johnson says.

TEST RESULTS

At the SAE 2016 World Congress and Exhibition, the following test report was presented by authors Arunandan Sharma and Fabien Redon: After having tested basic transient manoeuvers such as loadstep changes on the 4.9 litre

three-cylinder opposed-piston diesel engine, a similar test engine was subjected to a more aggressive test routine – a hot-start heavy-duty FTP (Federal Test Procedure) transient cycle for the on-road engines. The three main

objectives of this exercise were: 1) To assess the ability of the engine to meet the transient cycle requirements while maintaining close to the cycle-average BSFC for the FTP cycle derived from steady-state torque-tofuel map, 2) To

attain engine-out brakespecific emission levels that are compatible with the US2010 EPA requirements with a conventional after-treatment system consisting of a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF)
and a selective catalyst reduction (SCR) system, and 3) To compare hot-start FTP transient cycle fuel economy with a publicly available benchmark. 

The initial results from the test are encouraging – the BSFC value is within 1.2 per

cent of the value derived from running FTP cycle on a steady-state torque-to-fuel map. The engine-out emissions (BSNOx and BSSoot) levels generated during the test are compatible with US2010 EPA tail-pipe emissions

requirements and can be controlled with contemporary after-treatment systems. Furthermore, compared to the MY2011 Cummins ISB 6.7 litre engine, Achates Power’s OP engine presents a cycle-average BSFC advantage
of 18 per cent during hot-start FTP cycle. These results highlight the capabilities of the Achates Power OP engine to successfully run aggressive transient manoeuvers without compromising the required performance attributes.