Pinnacle Engines has developed an ultra-efficient engine design based on a four-stroke, spark-ignited (SI), opposed-piston, sleeve-valve architecture using conventional engine manufacturing technology. The company says that the architecture, developed in-house in conjunction with FEV, incorporates two old efficiency ideas into one package, improving both in the process.
Opposed-piston engines have been around for quite some time in two-stroke form but suffer from an emissions perspective. Sleeve-valve engines had some decided advantages in knock resistance and power density, but they too had emissions-related challenges due to the sleeves’ lubrication circuit.
The Pinnacle design addresses the problem areas for both architectures by combining and improving them. The use of sleeve valves enables a four-stroke cycle in an opposed-piston architecture, and the use of a novel sleeve valve that operates like a traditional poppet valve has allowed the lubrication circuit to be fully isolated from inlet/exhaust flow. The result is an architecture that provides better thermal efficiency through reduced heat loss, improved combustion, and a wider operating range.
The architecture addresses the global requirement for improved fuel economy at an affordable price. The company says that the “dollars per % improvement” metric for the architecture is dramatically better than competing technologies and is easily coupled with current state-of-the-art techniques for engine efficiency.
The engine architecture is said to be well suited to advanced configurations such as variable compression ratio (VCR), but the initial focus of this design is for developing countries where low initial cost is of paramount importance. Consumers expect payback on vehicle purchase price in a roughly 18-month time frame at current fuel prices and driving distances, which precludes solutions such as turbocharging, direct injection, variable valve timing (VVT), etc. Because a lower-complexity version of Pinnacle Engines’ architecture is best suited to market entry in the developing world, the design, testing, and development efforts have been strongly biased toward validating a naturally aspirated, fixed-compression-ratio (CR), fixed-valve-timing engine configuration. Testing has been conducted with engine build specification changes to find a match between the brake performance map and the vehicle drive cycle’s fuel usage.
The company says efficiency gains demonstrate 30% drive-cycle efficiency improvements in fixed-geometry applications for developing markets. In addition, simulations show up to 50% improvement when variable-geometry features—such as variable valve timing and low-cost variable compression ratio—are incorporated.
The result is a powertrain system that provides dramatic reductions in both fuel consumption and greenhouse gas emissions without increasing the vehicle cost or weight, while meeting existing and projected emissions standards. The engine architecture is easily scalable and inherently fuel-friendly, with significant efficiency gains running on gasoline, CNG (compressed natural gas), LPG (liquefied petroleum gas), or alcohol. The engine is approaching 1000 h of successful testing in verifying the above performance gains. The company will be launching its first product in conjunction with an Asian OEM in 2013.
Pinnacle will be providing details of the engine at its 2012 SAE World Congress exhibit and in the High Efficiency IC Engines technical session on April 24. See SAE Paper 2012-01-0378 (http://papers.sae.org/2012-01-0378) and check out the video at http://gigaom.com/cleantech/the-green-overdrive-show-a-super-efficient-engine-video/.
In the session and paper, company engineers provide insight into the fixed-geometry configuration of the 250-cm³ single-cylinder engine. A test cell was developed with a custom crank-angle-based data-acquisition system to allow friction testing and indicated cycle development. Incipient knock criteria were defined, and test results presented compare the opposed-piston’s indicated cycle performance to conventional single-cylinder engines.
At high loads, the opposed-piston engine uses the Cleeves cycle, an operating mode in which spark timing is highly delayed from best power spark advance, to enable knock-free operation at an elevated 15:1 compression ratio using 87 octane fuel. Data are presented for sleeve-valve operating temperatures, peak cylinder pressure effects, and exhaust gas temperatures. LogP-logV plots at key drive-cycle operating conditions highlight indicated cycle advantages of the opposed-piston sleeve-valve engine over two configurations of a comparison poppet-valve engine.
Data show that the architecture’s extended lean operating limits enable reduced drive-cycle emissions in a target vehicle. Indicated cycle performance using gaseous CNG/methane is presented. The engine has been developed so that, with the most basic configuration, light-load indicated efficiency improvements of 15-30% can be realized over conventional poppet-valve technology.