figgie said:
how is that possible?
it might jump a couple points (high 20/low 30) but the reason for the internal engines combustion low efficiency is because of all the heat loss, pumping losses and friction everywhere and namely rings v. cylinder walls.
I haven’t seen the reports from Toyota but BMW states that their new bi-turbo I6 with direct injection as seen 10% increase in fuel efficiency on the Euro test cycle and 5-15% increase in real word driving. That’s quite a jump.
http://www.greencarcongress.com/2006/03/bmw_unveils_new.html
Denso which helped design the D-4 (Toyotas name for direct injection) system for Toyota clams a 21% increase in fuel efficiency in their 3L motor in the Crown.
http://www.globaldenso.com/ENVIRONMENT/e-report/2000/pdf/09.pdf
This is along side a 5% increase in power
http://money.cnn.com/magazines/business2/business2_archive/2005/10/01/8359238/index.htm
This accomplished in two ways.
One, the atomizing effect of the fuel can cool the air temp inside the cylinder. This allows a higher compression ratio to be used without experiencing pre-detonation. This means less fuel is needed to achieve the same power. Also the atomization of fuel directly into the pressurized combustion chamber allows for a very homogeneous (smooth and even) mixture, this allows for a very efficient and complete burn.
Two, The precession of the injectors, the fact they are located inside the combustion chamber, and the design of the cylinder head and piston allows the shape and size of the cloud of fuel to be controlled. This in turn allows three different types of combustion to occur. (Taken from:
http://en.wikipedia.org/wiki/Gasoline_Direct_Injection)
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Ultra lean combustion mode is effective under normal running conditions, when little acceleration is required. The fuel is not injected at the intake stroke but rather at the latter stages of the compression stroke, so that the small amount of air-fuel mixture is optimally placed just near the spark plug. This stratified charge is surrounded by mostly air which keeps the fuel away from the cylinder walls for lowest emissions. The combustion takes place in a toroidal cavity on the piston's surface. This technique enables the usage of ultra lean mixtures with very high air-fuel ratio, impossible with traditional carburetors or even intake port injection.
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Stoichiometric combustion mode is activated for moderate load conditions. In this mode, fuel is injected during the intake stroke. The air-fuel mixture is homogeneous with the stoichiometric rates necessary for the catalytic converter to remove a maximum of the major pollutants CO and NOx from the exhaust gas.
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In full power mode, the air-fuel mixture is homogeneous as well and contains the maximum amount of fuel that is possible to ignite without knocking out, as defined by the compression ratio of the engine. The fuel is injected during the intake stroke. This mode activates at high load conditions and provides maximum output and torque.
In the ultra lean mode I have heard numbers thrown around for A/F ratios from 65:1 to 50:1. As you can imagine being able to sustain air-fuel mixtures like these can provide for some very good fuel efficacy. Running levels like that allow you to extract a very high level of energy from the least amount of fuel.
These motors have existed in the consumer market in Japan since 1996, maybe earlier. The reason they haven’t been brought over to the North American market is because our gasoline contains high levels of sulfur. This high concentration of sulfur will destroy the special catalytic converters used on direct injection systems. Special catalytic converters are needed because of the high NOx levels caused by burning ultra lean A/F mixtures. Until recently only California has had low sulfur gasoline, but a new federal regulation is forcing other states to change. So this is why we are finally starting to see some direct injection cars over here.
Here are a couple more good links on the topic at hand.
http://oee.nrcan.gc.ca/english/programs/Doc3e.cfm?attr=16
http://www.findarticles.com/p/articles/mi_m3102/is_5_124/ai_n14696335
