After Gutenberg

Subtitle: Swirled, Not Shaken

Advanced ignition timing, a higher compression ratio, and a higher turbo boost pressure, all increase engine performance and efficiency.

This time last year there were promises from MIT researchers, who formed a company called Ethanol Boosting Systems LLC. They promised that direct injection could result in a highly efficient, low cost improvement to internal combustion engines.

A short while later there was discussion of a high level subsequent to a post on Green Car Congress about a new four cylinder engine from Audi, which features:

1. Charge motion control
2. Gasoline Direct Injection
3. Turbocharger
4. Intake cam phaser

The discussion involved GCC commentators Rafael Seidl, Andrey and informer and a review of the commentary made me wonder whether ethanol might be injected instead.

Andrey notes that GDI currently works in follow manner:

1) On intake stroke part (about ½) of gasoline is injected and is homogeneously mixed with air, filling all combustion volume
2) On compression stroke second part of gasoline is injected and forms rich fuel cloud around spark plug.

Combustion of ethanol requires higher compression. Precise engine control plus EGR (Exhaust Gas Recirculation) can allow a compression ratio of 19.5 enabling the combustion of the air/fuel mix ranging from E100 to E50. According to Brusstar and Bakenhus, thermal efficiency approximately equal to that for a diesel is achievable.

Andrey notes:

Overall mixture is stoichiometric, so exhaust gases could be treated on three-way catalytic converter to comply with tight emission regulations in US and EU. As one familiar with theory of SI engines should know, rich mixture around spark plug allows higher compression ratio without risking detonation.

And, as this blog previously has noted, a feature of Gasoline Direct Injection, Common Rail Systems is high compression. Andrey continues:

On described Audi turbocharged engine compression ratio is very high – about 10. On recent naturally aspirated 2.8 liter 210 hp Audi engine with GDI it is 12. Together with VVT [Variable Valve Timing], it allows about 5% increase in torque and hp, and about 10% better fuel efficiency. No reduced pumping losses for this technology.

Along with high compression, such systems require precise delivery in very short time frames. Seidl notes:

The entire process of ignition and heat release must be executed extremely reliably and fairly predictably within ~45 degrees crankshaft (~3 milliseconds at 2400 RPM). For a typical combustion chamber geometry , that implies an average flame propagation velocity of ~16m/s.

Still, ultra-lean mixtures present the greatest challenge to flame development and completeness of combustion. Informer notes:

The ratio of specific heats of the working gas, which is influenced by the A/F ratio (not forgetting gas temperature and any participating gas compositions before and after combustion), is an important parameter in setting the upper bound on real engine efficiency. It is often forgotten that lean operation is more than just throttle and cylinder wall heat loss reduction.

One goal of a regulated turbine is to expand the usable flow rate range in practical applications while maintaining a high level of efficiency. To accomplish this, the turbine output is regulated by changing the inflow angle and inflow speed at the turbine wheel inlet. In the case of the VTG (Variable Turbine Geometry) turbocharger from BorgWarner Turbo Systems this is achieved using guide vanes located in front of the turbine wheel.

The current Wikipedia entry on variable geometry turbocharging indicates that recent development is with twin turbocharging. In another GCC post about Euro Tier 2 Bin 5 standards, Seidl commented to Andrey:

Porsche is so far the only company to have produced a gasoline engine with a VTG turbo; there are R&D efforts underway to bring this technology to less expensive vehicles as well. VTG would be useful in gasoline turbo engines precisely because it can compensate to some extent for the lower density of exhaust gases in throttled operation, minimizing turbo lag. This is critical for wider market acceptance of turbocharged gasoline engines with modest displacement and superior fuel economy.

This blog would observe that the internal combustion engines in the Aptera and proposed VW 1 liter car* can be quite small because the vehicles are lightweight and having very low coefficients of drag. Still some of the same principles apply, e.g., generally the more efficient the engine, the less emissions.

Note: The production VW 1 liter car supposedly will have a one-cylinder 300 cc engine. The microcar reportedly will go a top speed of 120 km/h and will sip 1-litre of fuel per 100 km travelled. “Such figures may sound ambitious,” observes GCC, “but back in 2002 Volkswagen developed a tandem-seater concept that consumed just 0,89-litres /100 km!

Furthermore, a big advantage when one chooses a Big Electric – Little ICE series hybrid drive train is flexibility in choice of range extender; such modular design means that you could use one type of engine now, and replace it with another means of generation that proved to be cheaper and cleaner.