Coban

iTrader: (14)

What has been keeping direct injecting gas engines from being widespread. What obstacles have to be overcome?

My understanding says that one would be able to run much higher compression ratios in a gas engine if the fuel was not in the cylinder with it. After all, at the same compression ratio, a gas engine is actually more efficient than a diesel.

MadBill

I don't believe there is any substantial advantage re max compression ratio. Once the fuel is mixed and ignited, it burns about the same regardless of where it was introduced. DI will support very lean, stratified charge combustion, which gives a big fuel economy advantage, but the resulting high NOx emissions flunk Canada/US standards, so DIs here manage only modest gains.

ConnClark

Gas direct injection runs into the same problem of getting a good fuel mixture throughout the cylinder that diesel engines do. Combustion likes to take place around the injector. This generates heat in a localized area which tends to generate a lot of NOx . You also have some of the same problems that turn off people to diesels , engine noise and vibration.

2002_Z28_Six_Speed

iTrader: (19)

I think DI is an added expense.

Honda likes to use it in the Asian market. Maybe because of emmision laws.

I just saw an article on a Lex engine that uses DI and port injectors. WHY go through all the expense? I have no idea. They claimed to pick up 7% power. They claimed the that the increased speed of the fuel flow (DI injector) helped solve a 'doldrum' area of the RPM range at which the car would cruise at.

andereck

Are direct injection gasoline engines not still spark ignited? If so I would think combustion would initiate at the spark plug. I would like to see a combustion space temperature graph vs. crank position without combustion as I would think that direct injection would allow the fuel to be introduced after the peak heat of compression occurs and spark timing could occur later improving parasitic motoring losses.

This I think would improve NVH. Maybe the high pressure delivery system is noisy, but that will be worked out in time.

ConnClark

If the whole point is to prevent knock from occuring at higher compression ratios the fuel most be injected toward the top of the stroke. The air temp also peaks at the top of the stroke. I think they are using a spark to ignite the air fuel mixture just as injection starts to take place to establish combustion before the bulk of the fuel enters the cylinder to avoid detonation. What you end up with is almost a diesel cycle.

andereck

Precisely why I think the fuel would best be injected right when the piston stops at TDC or very shortly before, time permitting. I don't see how the spark could be ignited during injection as that would ensure that the air/fuel mixture wouldn't be an air/fuel mixture. I could see an alternative fuel very high compression engine using ethanol to lower compression temps with a percentage of fuel injected well into the intake runner and the bulk direct injected. A 14-15 to 1 engine would be damn responsive and could possibly recover the mileage lost from the lower energy fuel.

ConnClark

At a certain point it just makes sense to move to a pure diesel cycle. It takes the limit off of what you can run as a compression ratio entirely. My mercedes runs at 21.5 to 1.

andereck

Then you're back to diesel fuel which runs at a slightly higher stoich point, thus containing more energy than gas. That and the lack of a throttle, why mess with gasoline at all then? 2 stroke diesels for everybody! Just doesn't sound sexy at all to me.

ConnClark

Yeah but you can run them off of just about anything. Corn oil, Lin seed oil, soy bean oil, peanut oil, rendered animal fat, and rendered fat from eco-weenies that grip about diesel soot and NOx.

In finland there are guys getting 400+ HP out of 3 liter diesels http://www.teamrwd.com/dieselboost/v...dslboost05.wmv

Edit: Dyno chart http://www.teamrwd.com/dieselboost/merssu1.jpg

joecar

Will they run on used engine oil, used atf and used gear oil...?

MrMiracle

Last issue of Car Craft showed the next generation of Ecotec is supposed to use direct injection. I didn't think much of it at the time.

bigredexpress99

iTrader: (15)

the pontiac soltice gtp and saturn sky redline with their turbo engines use direct injection.

ConnClark

I have heard of people drivng mercedes 300SDLs (which was mercedes first aluminum head diesel) have a head gasket blow and the engine ran up and wouldn't shut off. I suppose its possible, not that I would try it. There is a reason you don't want old oil in your car any more. All the crap that is held in suspension in it isn't going to stay suspended when the oil burns away. Gear oil might just barely work but I can't imagine it would run well. High viscosity fluids are tough to atomize. I don't think atf would work.

niphilli

The new BMW turbo inline six is also using it.

Can someone here explain exatly what direct injection is?

Old SStroker

Audi uses DI on a few current production engines. They did well with their R8 LeMans DI gasoline engines for the last few years. The got about one more lap per fill up than the competition.

For high performance engines DI allows more mass of air to get into the engine because fuel isn't taking up some of the space. Another advantage is that you are not blowing fuel out the exhaust during valve overlap in the (lower) rpm ranges where that occurs.

DI requires high fuel pressures. F1 is being limited to 100 Bar (1470 psi). Some F1 engine builders tried fuel pressures up to 500 Bar, but didn't go to DI even before the 100 Bar limit. Getting a fuel pump to do very high pressure efficiently with gasoline is a challenge. Diesel fuel lubricates the fuel pump, but gas just cleans it out and lets it heat up.

NHRATA01

iTrader: (10)

Correct me if I'm wrong, but I believe another of the benefits of DI is that the atomization, and evaporation of the liquid gasoline helps to cool the combustion chamber during the process, poviding additional detonation resistance over a conventional injection setup.

chuntington101

yeah you have to run really high injector presure. this really helps with atomization and thus more power and better fuel econamy!

Audi are using DI in their new V10 (nicked form the lambo) and its pretty good!

Chris.

CATransam

Mercedes and BMW engines are all going the route of direct injection. Issuzu is also working on them for the GM full size trucks.

niphilli

Found it on another site...The basic is that the fuel is injected directly into the combustion chaimber instead of into the intake port or into the manifold port.