High Performance AND Fuel Economy (794)


This week we’re looking at some insight on High Performance AND Fuel Economy. Is it possible?

Well I can’t think of anyone more qualified to share his view on the matter than colleague and friend Merkel Weiss. Regular readers of the column will recognize the name and may recall he is an automotive engineer who has worked for Chrysler in his younger years and a professor of automotive design at the prestigious Pasadena based Art Center College of Design right above the Rose Bowl in Pasadena, California.

Herewith is Merkel’s informative view of where car power plants need to go in the future.

Call off the funeral –

the IC engine isn’t dead yet. It’s not even sick, says Merkel Weiss
As the political winds blow toward the ecology yet again, I’m reminded of how we have so often looked for the combined qualities of emissions, power, and fuel economy in our automobiles. As engineers, we’re accustomed to asking why we can’t have it all. And while we’re at it, let’s just throw in braking and handling too. So in short, why can’t I have a car that looks and drives like a Maserati and get the fuel economy of a Prius? Be careful what you wish for and make sure that you have the priorities straight or you just might end up with a car that looks and drives like a Prius and has the fuel economy of a Maserati.

I have never been a big hybrid fan although I had a role in building the first modern hybrids at JPL in the 80’s; we built a flywheel/electric and a gasoline/electric car with the help of VW and GE. They were infinitely less sophisticated than today’s Toyota Prius but they do have the one thing in common. Ask if it’s fun to drive and the response will be that it’s got great fuel economy. Well, we can have it all and here is how it will most likely go down in the next 10 years.

The first step is to put our cars on a low carb diet. No, not twin low profile carburetors under the hood, it means that it’s time to thin down. It’s time to lose the baby fat that has accumulated from the tried-and-true method of improving crashworthiness by slathering metal all over the place, what I call the IIHS school of design.

Let’s get back to some actual engineering and use cost and weight reduction principles to maintain the crash performance while reducing the bulk by about 30%. This is a serious task but the dividends are vast. Slap on the rack and pinion steering along with big tires, wide rims and big brakes and most modern cars will become slot cars in big scale. Lower weight almost always rules out a hybrid vehicle as a result of the fact that batteries are heavy.

But then there’s that fuel economy question. It’s never really been done after all, the high performance fuel economy car. Is there a market for it, or are we merely pursuing undomesticated ornithoids (wild goose chase)? You bet there is. It’ll sell like crazy if the price is right. It all depends on the engine.

Engineers tend to think of an engine characteristic called BSFC, Brake Specific Fuel Consumption given in units of pounds-mass of fuel per hour, per horsepower generated. This amounts to how much fuel is burned to generate each horsepower. We want lower BSFC to do the job here, so let’s have a look at what we have on the plate at the moment. Spark ignition engines have a reasonable baseline at about 1.0 – 0.5, while diesel engines are known to be significantly better at 0.8 – 0.35 (lbm/hp-hr). It has been said that diesel engines perform about 30% more efficiently than spark engines do, and the BSFC charts seem to confirm the truth in that. The difficulty has always been with emissions however. As a result, a new type of engine will shortly make an appearance which is a combination spark and diesel engine. The device is called HCCI (Homogeneous Charge Compression Ignition) and it will run as either type. For example, in June of 2008 Mercedes Benz has shown a prototype car called the F700 Concept with what they call a DiesOtto, a 1.8 liter supercharged engine with 238 hp.

But wait, there’s more. The holy grail of engine design for the past 100 years has always been the electronic control of the valves. Each cylinder needs to run as if it were its own one-cylinder engine, while at the same time the valve timing needs to be optimized for conditions, demand, emissions and BSFC. The auto industry is very near the technological place where this can happen, but at the same time there are a few other possibilities which, if executed with some engineering art, can turn the engine into high performance/fuel economy. The turbocharger and charge air cooler of the HCCI engine need to be scientifically optimized for road speeds that make sense, unlike the current crop of 250 mph supercars. Where exactly do you drive at 250 mph? A limiting speed of something more rational is long overdue and allows for a far more useful overall design.

The unique cylinder computer control over all 4 valves allows the use of late closing of the intake valves (as in the Miller Cycle) for optimized economy and, at the same time, the near instantaneous switchover from 4-stroke per cycle to 2-stroke per cycle for maximum horsepower. In this way, I can envision a 4 cylinder, turbocharged 1.6 liter 4-valve double overhead cam engine with discrete valve timing that is capable of achieving about 320 hp. Installed in a car that weighs about 2300–2500 lbs. should give a 0 – 60 time of about 3.8 seconds and 45mpg.

You think there’s a market for that?

Your comments are welcomed. My e-mail is joe@autolove.com
Copyright © 2010 – An Automotive Love Affair

Your comments are welcomed. My e-mail is joe@autolove.com
Copyright © 2014 – An Automotive Love Affair.