Prev: P0171/P0174 Help!
Next: LTFT1 & LTFT2....ford truck
From: C. E. White on 18 Jul 2008 11:05 "EdV" <systmengr(a)hotmail.com> wrote in message news:2e0036d7-156b-4b0e-9625-11ef7fab6a74(a)i36g2000prf.googlegroups.com... > This is how I understand GDI (gasoline DIRECT injection), feel free > to > correct my mistake > > Fuel and air mixture are injected in some kind of pressure tank > where > the pressure is increased, by compressing the mixture I suppose. At > this stage the ratio of the fuel and air is adjusted for optimum > burn. > > This pressure tank sometimes called as a *common rail*? has a nozzle > that will release the pressurized fuel-air mixture directly into the > chamber chamber via the intake valves. This high pressure coupled > with > optimum ratio allows the engine to run more fuel efficiently and, of > course, more powerful. The VVTi (toyota) will then adjust the > opening > of the valves whether to inject the mixture during the intake stroke > or slightly delayed. In the direct engine engines I have researched, there is no tank that mixes the fuel and air. There is an injector in the combustion chamber instead of in the intake tract before the intake valves. Air is admitted into the combustion chamber by the valves. Fuel is injected directly into the combustion chamber, instead of being mixed with the air in the intake tract before the intake valves. By injecting the fuel directly into the combustion chamber, you can create a "stratified charge." In other words a non-uniform mixture of gasoline vapor and air. Gasoline is very difficult to ignite if you don't have the proper air/fuel mixture. By creating a stratified charge, you can have a proper A/F mixture in the area of the spark plug and a lean mixture everywhere else. The spark plug can then easily ignite the proper mixture in the area of the spark plug and this in turn will burn the leaner mixture elsewhere in the combustion chamber. This allows an overall leaner mixture to be burned, resulting in higher efficiency. Chrysler tried this years ago with carbureted engines with limited success (tried to manipulate the mixture with combustion chamber and intact tract shape). Honda tried something a little different with a three valve design in the late 70's (two "regular" valves and one smaller valve to richen the mixture near the plug). Neither worked very well. There are a lot of great claims being made for direct injection engines. However, the direct injected manual transmission Mazda 5 gets worse EPA gas mileage than the regular old 4 cylinder automatic Toyota RAV4 (which is larger and heavier...). Ed
From: EdV on 18 Jul 2008 11:36 On Jul 18, 11:05 am, "C. E. White" <cewhi...(a)removemindspring.com> wrote: There is an injector in the combustion chamber > instead of in the intake tract before the intake valves. Air is > admitted into the combustion chamber by the valves. Fuel is injected > directly into the combustion chamber, instead of being mixed with the > air in the intake tract before the intake valves. Ahh, so the intake valves is just for the AIR and the injector for the FUEL. no pre-mixing involved. The mixing occurs directly inside the combustion chamber. The fuel is pressurized and not the air like in a turbo setup. Thanks!
From: Retired VIP on 18 Jul 2008 14:16 On Fri, 18 Jul 2008 08:36:01 -0700 (PDT), EdV <systmengr(a)hotmail.com> wrote: >On Jul 18, 11:05 am, "C. E. White" <cewhi...(a)removemindspring.com> >wrote: > There is an injector in the combustion chamber >> instead of in the intake tract before the intake valves. Air is >> admitted into the combustion chamber by the valves. Fuel is injected >> directly into the combustion chamber, instead of being mixed with the >> air in the intake tract before the intake valves. > >Ahh, so the intake valves is just for the AIR and the injector for the >FUEL. no pre-mixing involved. The mixing occurs directly inside the >combustion chamber. The fuel is pressurized and not the air like in a >turbo setup. Thanks! Yep, you got it Edv. But the fuel is injected into the combustion chamber, not the intake manifold. Of the three types of fuel injection, the direct injection has the capability of being the most efficient. The air/fuel mixture can be precisely adjusted for each individual cylinder and for each individual power stroke. Throttle body injection is the least precise of the three. It is basically just a computer controlled carb that uses a injection jet instead of a metering jet. It's better than a carburetor but not by much. Multi-port injection places one injector in the manifold runner to each cylinder. This is a better scheme that allows more precision but it is limited on how much the mixture can be leaned out before pre-ignition occurs. Direct injection allows placing a rich fuel/air mixture around the sparkplug and a much leaner mixture in the rest of the cylinder. By the time the flame front moves out to the rest of the cylinder, the piston has moved past top dead center and the much faster burn rate of a lean mixture won't hurt the engine. I hope this helps and if I've gotten anything wrong in this, I'm sure someone will correct me. Jack
From: EdV on 21 Jul 2008 09:35 On Jul 18, 2:16 pm, Retired VIP <jackj.extradots....(a)windstream.net> wrote: > On Fri, 18 Jul 2008 08:36:01 -0700 (PDT), EdV <systme...(a)hotmail.com> > wrote: > > >On Jul 18, 11:05 am, "C. E. White" <cewhi...(a)removemindspring.com> > >wrote: > > There is an injector in the combustion chamber > >> instead of in the intake tract before the intake valves. Air is > >> admitted into the combustion chamber by the valves. Fuel is injected > >> directly into the combustion chamber, instead of being mixed with the > >> air in the intake tract before the intake valves. > > >Ahh, so the intake valves is just for the AIR and the injector for the > >FUEL. no pre-mixing involved. The mixing occurs directly inside the > >combustion chamber. The fuel is pressurized and not the air like in a > >turbo setup. Thanks! > > Yep, you got it Edv. But the fuel is injected into the combustion > chamber, not the intake manifold. > > Of the three types of fuel injection, the direct injection has the > capability of being the most efficient. The air/fuel mixture can be > precisely adjusted for each individual cylinder and for each > individual power stroke. > > Throttle body injection is the least precise of the three. It is > basically just a computer controlled carb that uses a injection jet > instead of a metering jet. It's better than a carburetor but not by > much. > > Multi-port injection places one injector in the manifold runner to > each cylinder. This is a better scheme that allows more precision but > it is limited on how much the mixture can be leaned out before > pre-ignition occurs. > > Direct injection allows placing a rich fuel/air mixture around the > sparkplug and a much leaner mixture in the rest of the cylinder. By > the time the flame front moves out to the rest of the cylinder, the > piston has moved past top dead center and the much faster burn rate of > a lean mixture won't hurt the engine. > > I hope this helps and if I've gotten anything wrong in this, I'm sure > someone will correct me. > > Jack Great! So this means its possible not to have VVTi and Direct injection at the same time. The timing of the fuel comes from the nozzle and not from the opening of the valves, although air enters through the valves, its the fuel which is controlled and not the air.
From: Retired VIP on 21 Jul 2008 16:54
On Mon, 21 Jul 2008 06:35:30 -0700 (PDT), EdV <systmengr(a)hotmail.com> wrote: >On Jul 18, 2:16 pm, Retired VIP <jackj.extradots....(a)windstream.net> >wrote: >> On Fri, 18 Jul 2008 08:36:01 -0700 (PDT), EdV <systme...(a)hotmail.com> >> wrote: >> >> >On Jul 18, 11:05 am, "C. E. White" <cewhi...(a)removemindspring.com> >> >wrote: >> > There is an injector in the combustion chamber >> Direct injection allows placing a rich fuel/air mixture around the >> sparkplug and a much leaner mixture in the rest of the cylinder. By >> the time the flame front moves out to the rest of the cylinder, the >> piston has moved past top dead center and the much faster burn rate of >> a lean mixture won't hurt the engine. >> >> I hope this helps and if I've gotten anything wrong in this, I'm sure >> someone will correct me. >> >> Jack > >Great! So this means its possible not to have VVTi and Direct >injection at the same time. The timing of the fuel comes from the >nozzle and not from the opening of the valves, although air enters >through the valves, its the fuel which is controlled and not the air. No, I think it would still be possible to use variable valve timing and direct injection at the same time. The amount of fuel is controlled by the engine computer based on info it gets from the O2 sensor, throttle position, RPM, etc. VVTi would still be a valid way to increase engine efficiency by controlling the amount of air, that's really all it controls with multi-port injection also. Jack |