Under Pressure: Octane and Compression Ratio News

At this year’s SAE World Conference, participants were told that automotive engineers will need higher octane fuel in order to meet upcoming emissions and mileage standards. Regular gas in the US is rated 87 octane while premium carries an octane rating of 93. But in Europe, gasoline has an 95 octane rating. That’s what tomorrow’s engines will require, the engineers say. Higher octane fuel burns cleaner and produces more power. Today’s turbocharged engines often utilize a compression ratio of up to 12:1.

Variable connecting rod for different compression ratio

The kicker is that premium unleaded already costs about 50 cents a gallon more than regular. Gasoline with a even higher octane rating would cost more than that. Americans seem to believe they have a God given right to cheap gas though the seas may rise and the heavens may fall. One of the reasons the federal gas tax has not been raised since the Clinton administration is because no politician wants to be the one to tell constituents the price of gas is going up. Everybody talks about climate change but nobody wants to actually do anything about it.

On a related note,  Dean Tomazic, executive vice president and chief technical officer for FEV North America told the SAE engineers about an innovative engine design his company has been testing. Similar to the cylinder deactivation technology now in use in many internal combustion engines, the FEV device allows the length of a connecting rod to vary according to the demands placed on the engine.

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.

Such a system would also be ideal in dual fuel engines that can operate on either gasoline or compressed natural gas. CNG permits higher compression ratios. An engine with the FEV variable connecting rods could adapt itself to either fuel. Tomazic says engines using FEV’s new technology are powering test vehicles today and could be ready for production in about 3 years.

We did a story recently about Jeff Bonner, a mechanical engineer and inventor in Florida who wants to replace the traditional crankshaft with cams. Bonner says his idea would also lower emissions and boost power without consuming any more fuel than a normal engine. Several comments dismissed Bonner’s idea, saying that the world is transitioning to electric propulsion and it is foolish to waste any more time and money on developments to the internal combustion engine.

But the truth is, the ICE will be with us for decades more. Even the most optimistic assessments don’t expect more than half the cars on the road to be EVs 20 years from now. A fully electric transportation world won’t happen for decades after that. In the meantime, the ICE will still be used in millions of conventional cars and the plug in hybrids each year. Any ideas that will make them burn cleaner and more efficiently should be fully explored.

Photo credit: FEV North America


Steve Hanley

Closely following the transition from internal combustion to electricity. Whether it's cars, trucks, ships, or airplanes, sustainability is the key. Please follow me on Google + and Twitter.