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FEV analysis of automotive-scale Pinnacle opposed-piston engine finds potential for significant increases in fuel economy
15 May 2013
An analysis by FEV of a modeled automotive scale version of Pinnacle’s 4-stroke, spark-ignited (SI), opposed-piston, sleeve-valve architecture engine (earlier post) concluded that the engine has the potential to deliver significant additional fuel economy benefits of up to 42.6% with application of various advanced technologies over a baseline naturally aspirated (NA) 1.5L configuration of the engine.
Start-up Pinnacle initially has been targeting the Asian two-wheeler market with a small-displacement version of its technology (e.e., 110 cc) to gain some market traction rather than trying to push its way into the automotive market. Automotive, however, has always been a company target, notes founder Monty Cleeves. FEV is also supporting Pinnacle on those initial versions of the engine.
The goal of the studies was make a preliminary assessment of Pinnacle Engines suitability for automotive applications based on the work-to-date on the small single-cylinder engines. FEV conducted three programs to assess fuel economy potential; technical and manufacturing feasibility; and cost.
The new and unique features of the Pinnacle Engine present significant performance potential, addressable engineering challenges, and expected production costs. The design merits continued development for automotive application.—FEV analysis
Fuel economy. The fuel economy study, using GT Power, encompassed both a naturally aspirated 1.5-liter, 3-cylinder design of the Pinnacle engine, as well as a downsized, turbocharged 750cc Pinnacle design.
To build the GT Power models for the engine, FEV used an existing model of the 250cc single cylinder engine as a starting point, then modified it to be used predictively by adding lookup tables for 50% burn location, 10-90% burn duration, liner and piston temperatures based on engine speed, IMEP, and the lambda value.
FEV added two additional cylinders, piping, exhaust aftertreatment, and an air cleaner to convert the model from a 250cc single cylinder into a 750 cc three cylinder engine. To predict fuel economy for the baseline 1.5L Naturally Aspirated (NA) modeling, FEV used two times the fuel used in a 750cc NA model.
FEV investigated the impact of six fuel saving technologies: friction reduction; turbocharging; Variable Compression Ratio (VCR); Variable Cam Timing (VCT); Early Intake Valve Closure (EIVC); and downsizing. The predicted fuel economy of the base Pinnacle engine, over the full drive cycle, was 37.3 mpg US (6.3 l/100 km). As a point of baseline comparison, an unnamed production MY2009 1.5L I4 PFI conventional engine selected as appropriate for the analysis offers combined fuel economy of 29.4 mpg US (8.0 l/100km.)
Friction Reduction. Pinnacle Engines estimates a possible reduction in FMEP of 0.35 bar due to differences between the prototype geometry and proposed production layout. Applying this reduction to the model resulted in a significant fuel economy improvement of 8.8% (40.6 mpg US, 5.8 l/100km).
Turbocharging. Boosting the engine through either turbocharging or supercharging allows improved fuel economy through downsizing or downspeeding the engine. In this study, the turbocharger was investigated with and without downsizing. Added to the 1.5L engine, turbocharging resulted in a 0.5% increase in fuel economy (37.5 mpg US, 6.3 l/100 km). Acceleration and top speed performance would also improve.
Variable Compression Ratio (VCR). The architecture of the Pinnacle opposed piston engine is well suited to the addition of a VCR system. This may be done through the use of a phaser, similar to the ones used to adjust the timing of a camshaft in a VCT system. The phaser for a VCR system requires a higher torque capacity than the VCT system.
FEV investigated a range of ratios from 8 to 25, resulting in up to a 3.2% improvement in fuel economy (38.5 mpg US, 6.1 l/100 km).
Variable Cam Timing (VCT). Variable cam timing maintains the lift and duration profile of the cam, but changes the timing of the events to earlier or later. FEV explored addition of VCT for both the intake and exhaust cams, and for intake only. Acceptable timing combinations were limited to those with residual gas fraction (RGF) levels below 15%.
FEV found a benefit of up to 3.8% (38.7 mpg US, 6.07 l/100 km). FEV found the main benefit of VCT with the intake cam phasing, with a resulting improvement of 3.5% (38.6 mpg)—just 0.3% less than with the exhaust cam also phased. AS a result, FEV suggested cost savings may be found by only using a phaser on the intake cam.
Early Intake Valve Closure (EIVC). Shortening intake valve duration and lift while maintaining the same opening timing is another method for improving fuel economy. A variable valve lift system combined with a phaser to maintain the opening event would enable the EIVC.
Pinnacle developed two valve profiles to represent early intake valve closure; in production this would be accomplished through a combination of variable valve lift and variable cam timing. The result was a fuel economy improvement of up to 5.9% (39.5 mpg US, 5.96 l/100 km).
VCR and EIVC combination. FEV investigated the level of benefit of both adding VCR and EIVC by analyzing a sweep of compression ratios for the EIVC cams. Fuel economy improvement was up to 8.0% (40.3 mpg US, 5.8 l/100 km).
If the individual benefits of each are summed, it gives 5.9%+3.2%=9.3%, 1.3% more than what is seen when they are combined in the model. The benefits of the two technologies are not purely additive, and have some overlapping benefit.
Downsizing with turbocharging. To maintain the same power at a given engine speed with a smaller engine, a higher BMEP is required proportional to the reduction in displacement. The higher BMEP condition reduces pumping losses, improving the fuel economy.
The downsized 0.75L configuration showed a significant 33.5% improvement over the 1.5L NA baseline engine.
Downsized turbo with friction reduction. FEV found that combining reduced friction levels with the downsized turbo model resulted in an improvement of 42.6% over the 1.5L NA baseline.
Turbocharged with VCR. FEV also combined VCR with the downsized turbocharged model and found an improvement of up to 40.5% over the NA baseline (52.4 mpg, 4.49 l/100 km). However, peak cylinder pressures in one of the points neared known knock limits in the current engine. When this engine point is limited to known safe pressures, the resulting fuel economy improvement is 36.7% (51 mpg, 4.61 l/100 km) .
Overall, the analyses found the largest improvement in fuel economy is through downsizing and turbocharging of the engine. Combining downsizing, turbocharging and friction reduction, the simulation results show the potential for 42.6% improvement in fuel economy over the 1.5L NA version of the Pinnacle engine.
Cost and technical feasibility. The cost study used a 3-cylinder, 1.2L Pinacle configuration, chosen as the most likely initial displacement that the company would be targeting, said Tom Covington, Pinacle’s VP Marketing and Special Projects. The 1.5L engine was chosen for the GT power study because FEV had benchmarked the 1.5L recently, he noted. The cost delta between a 1.2L and a 1.5L would be a function of material cost differences, and should scale appropriately, he said.
The FEV analysis compared the 1.2L Pinnacle engine to a modeled 1.2L I4 baseline engine. FEV found that the 1.2L Pinnacle engine would cost $192 (17%) more than the baseline: $1,133 vs. $941, mainly due to the need for a higher quantity of some key components such as pistons, crankshaft, and so on. (E.g., a three-cylinder Pinnacle engine uses six pistons.) The 17% cost delta assumes similar content levels (VVT, PFI), with the additional feature of VCR on the Pinnacle engine design.
The engine also contains new and unique design considerations and failure modes; those, however, can be addressed in a traditional automotive design and validation program, according to FEV.
Engine packaging and installation is a “somewhat unique feature” of the Pinnacle engine, FEV noted, with the horizontal cylinder arrangement potentially presenting some limits in terms of the number of current vehicles that could accept the engine. FEV expanded the study to consider an alternative, vertical installation.
FEV’s analysis found that while the Pinacle engine has additional potential failure modes not evident in current production engines, addressing those failure modes are well within the scope and capabilities of current analytical tools and testing techniques.
FEV estimated it would take 54 months to bring an automotive version of the Pinnacle Engine into production.
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