FEV VCR Technology May Suit Natural Gas Engines

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.

NGS INDIA