The FEV Group, an internationally recognized powertrain and vehicle engineering company, has presented a 3-cylinder technology demonstrator mock-up at the 2016 SAE World Congress at Cobo Center in Detroit this week. The mock-up highlights a combination of innovative technologies for down-sizing and down-speeding engines and features 2-stage variable compression ratio (VCR) – a technology suitable for higher octane alt-fuel applications such as Compressed Natural Gas (CNG).
FEV says that in SI engines – especially when running on alternative fuels such as CNG – average peak pressures (p_max_mean) of up to 170 bar dramatically increase the tendency toward combustion knocking at higher engine speeds. One measure to tackle these limitations involves varying the compression ratio during engine operation.
According to an NGV Global technical adviser, the VCR technology could find future application for bi-fuel natural gas vehicles (NGVs). An increased compression ratio for natural gas operation is desired to take advantage of the higher octane levels of cleaner-burning natural gas.
Dean Tomazic, Executive VP and CTO, FEV North America, told Automotive World in 2015: “We have developed two different systems – a continuously variable compression ratio mechanism, and a two-step. The two-step is essentially a simplified version – it is both easier and cheaper to incorporate, so we are seeing a lot of interest among our customers and several programs are on-going because of the high potential of such a technology to meet fuel economy and CO2 targets.”
Tomazic contined the theme at this week’s SAE World Congress. According to Ward’s Auto, “The system uses two internal valves in the connecting rod to vary the con-rod length to change the compression ratio depending on load, improving thermodynamic efficiency, he explains. The system is not infinitely variable but shifts between two preset ratios that can vary the compression ratio in a 4-point range.” The net effect is an estimated 3% to 6% reduction in carbon dioxide emissions and a similar improvement in fuel economy, Tomazic says.
“In a bi-fuel gasoline/CNG engine, the system automatically would shift to the higher compression ratio when running on CNG, avoiding the typical power and efficiency losses incurred when running CNG in a gasoline engine with a set compression ratio,” Ward’s Auto further explains.
Ward’s Auto reports from the SAE event the VCR technology is undergoing field trials in both Europe and the U.S., and is headed for production within three years.
VCR Control Patent Abstract (WIPO Patent Application WO / 2016/016202)
FEV GMBH submitted a patent application, published Feb 04, 2016. The patent abstract states:
A method for switching an adjustable compression ratio of an internal combustion engine (1) having an adjustment device for the adjustment of the adjustable variable compression ratio in at least one first cylinder and one second cylinder with a first compression ratio of the first cylinder and a second compression ratio of the second cylinder, wherein, in a manner dependent on a demanded load of the internal combustion engine, preferably in a manner dependent on at least one load demand signal, a torque to be output by the internal combustion engine (1) is determined, and, in a manner dependent on the torque to be output, in particular taking into consideration a mean pressure to be generated in the first cylinder, a first target compression ratio for the first cylinder and a second target compression ratio for the second cylinder are determined, wherein the first target compression ratio differs from the second target compression ratio, and the first compression ratio and the second compression ratio are adjusted to the first target compression ratio and to the second target compression ratio respectively.
(Sources: FEV, Ward’s Auto, Automotive World, WIPO)