Gasoline Direct Injection

[SHIPCHIEF]

Ross, I agree with your comment on advances in diesel engines in the new diesel thread;
However, IC engines are changing very fast. I believe the Gas Direct Injection engine is clouding the difference between the CI and SI engine, to the point that it will encompass the best features of both, and run on both fuels too.
http://www.automobilemag.com/feature...ion/index.html
This link shows a pic and describes GDI.
Take your considerable knowledge and extrapolate from there. Think about old semi-diesels, hot bulb engines and 'oil' engines, which were crude multifuel engines, then think about the changes that occured over time.
At first, refined engines required more refined fuels, but now refined engine controls allow more flexible fuel types, including blends.
High compression GDI could be both a diesel, and a gas engine. As soon as the engine bangs off a few strokes, the enigine managment system will analize the sensor data and tune the engine for whatever fuel.
It will be great, you can buy fuel based on cost per BTU. Solid foundations like the W-120 could be the future for MF-DI flight engines. Perhaps the Revetec engine would succeed and be such an engine.

[rv6ejguy]

Yes, I've discussed DI SI engines here several times over the last couple years and the efficiency gains possible. BMW has experimented with Valvetronic (no throttle plate) and DI on SI engines and said they can achieve BSFC figures as good as the latest auto diesel designs at light load cruising conditions. In 2006, the SAE World Congress saw great promise here with these technologies and the future of the SI engine: "2006 SAE World Congress "Turbocharged GDI engines currently in development are showing BSFC equivalent to diesels".

Most new auto manufacturers are selling some GDI models now and some of these engines have pretty amazing specs. They are able to run very high CRs on 87 octane fuel to boost the thermal efficiency. 12-13 to 1 CRs are not uncommon these days.

The new 3L BMW N55B30 engine has GDI, turbo and Valvetronic 295lb/ ft from 1500 to 5000 rpm and a 7000 rpm redline. Supposed to get exceptional fuel economy.

GDI opens many new possibilities for sure. I'd never thought of a dual cycle engine actually.

[Andy_RR]

GDI is solving a problem in the automotive arena that aircraft just do not have - i.e. fuel efficiency at light loads. Whilst the latest automotive GDI's may or may not be as good or better than diesel engines BSFC-wise at light loads, for aircraft it is irrelevant.

Also, GDI operates at much lower pressures than equivalent common-rail diesel systems. GDI runs from 50-120Bar (725-1750psi), whereas CRD's are running in excess of 2000Bar (29000 psi). That's an order of magnitude different, so don't expect to see multi-fuel SI/CI engines any time soon.

On the other hand, my old employer, Orbital Engine Company, has been promoting it's "Flex-DI" concept which is entirely spark-ignition, but capable of running from gasoline to heavy-ish fuel oils with the same hardware. Apart from fuel-sourcing versatility, I can't think of much of a reason why you'd want the compromise though...

A

[kristoffon]

Am I correct in understanding that GDI engines can operate on jet fuel, or is a diesel cycle required?

[terrye]

Don't forget another problem that automotive manufacturers have that aircraft don't: emissions regulations. They MUST meet these regulations first and foremost. Most of the technology that has been applied to automobile engines, including computer control, variable valve timing, turbocharging, etc. is aimed at meeting the emission regulations and also providing high specific output and part throttle economy. Remember the first generation of emission controlled cars in the 1970s? Thermal injectors, low compression ratios, exhaust gas recirculation, retarded ignition timing and low power coupled with poor driveability. Constant development has resulted in the very powerful and clean engines of today.

I do believe that some of the current automotive engine technology (SI or CI) can benefit aero engines, but the low production quantities of aero engines seems to work against its adoption.

What I can't figure out is why the aviation world has embraced the revolution in avionics over the last two decades, but not in engine technology? I've seen lots of panels that are worth as much as an engine, so it isn't just the money.

[Andy_RR]

Originally Posted by kristoffon

Am I correct in understanding that GDI engines can operate on jet fuel, or is a diesel cycle required?

A few can, but they are still spark-ignition, so the benefit of diesel cycle efficiency is lost.

[kristoffon]

Originally Posted by Andy_RR

A few can, but they are still spark-ignition, so the benefit of diesel cycle efficiency is lost.

But the benefit of cheap jet-a is gained

[Rotary10-RV]

Originally Posted by kristoffon

But the benefit of cheap jet-a is gained

Kristoffon,
Without the 20:1 compression ratio the Jet A doesn't provide as much power so you end up burning more. Also since it is heavier, if you don't get top efficiency with it Jet A would be a lose-lose situation.
At least where I live it doesn't make sense.
Bill Jepson