Internal Combustion

August 7th, 2009

Those who know me, and those who read this blog (yes, both of you) know that I am bullish on powertrain electrification.  The truth is, though, that virtually all of the cars on our roads today have internal combustion engines, and it will be that way for quite some time.  Fortunately, the internal combustion engine has come a long way from where it started, and it still has a long way to go.  And although the average fuel economy of vehicles in the U.S. has stagnated over the past couple o’ decades, the engines themselves have become much more efficient, moving around more and more mass at ever greater speeds without an increase in fuel use.

2010 Porsche 911 GT3

2010 Porsche 911 GT3

Recently, I was reading an article in Panorama (the official magazine of PCA) about the 2010 Porsche 911 GT3, whose 3.8 liter engine makes 435 hp.  That’s  114.6 hp/liter!  Not so long ago, the 100 hp/liter barrier was nearly impossible to breach, without using forced induction, but the GT3 blows right through it.  How did Porsche do it?  Well, for one thing, they rev it up to 8400 rpm, and to keep it from disintegrating when it gets there they use forged pistons, titanium rods, and light-weight tappets to actuate the valves.  They use variable valve timing and lift to optimize both the intake and exhaust valves across all regions of the rev range.  They use a variable intake manifold, again to optimize the timing with which the incoming pulses of air reach the backs of the intake valves at various revs.  They use a high compression ratio of 12.0:1.  The whole process is controlled through a sophisticated engine management system which constantly monitors conditions and precisely adjusts any variable related to combustion.

Of course, many of these tricks aren’t confined to high-end sports cars like the GT3.  Many production cars these days using variable valve timing, and variable intake manifolds are becoming mainstream as well.  Another technology with the GT3 eschews, but which auto makers are employing, is direct-injection of the fuel into the combustion chamber, resulting in more control of the combustion process.

Coming down the pike, we see efficiency improvements through technologies like variable compression ratio, such as that demonstrated by MCE-5; GM’s homogeneous charge compression ignition (HCCI), which combines concepts of both spark-ignition and diesel engines; and Fiat’s MultiAir technology, which very precisely controls the valve timing of each cylinder individually.  Combining these efforts with smaller engines using forced induction, such as Ford’s Ecoboost effort, may yield fuel efficiency improvements that go beyond today’s hybrids.  (And the technology compounds – the use of turbos means the ability to use variable turbine geometry!)

Internal combustion engines these days are a far cry from what they were 30+ years ago, when carburetors used low-pressure air to suck fuel out of a hole, and ignition timing was controlled through the centrifugal force of a couple of weights attached to the distributor.  …It will be a long time before we’re all driving pure electric vehicles.  And let’s face it: even PHEVs (and EREVs) have internal combustion engines.  So, let’s hope the advances continue!

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