TLDI, how does it work?

Author Message   Steve Member Username: wh500special Post Number: 7 Registered: 09-2006 Posted on Tuesday, November 27, 2007 - 11:44 pm:    OK, the title of this message was a little ambiguous but I have a question to, hopefully, placate my curiousity about these engines (and other DI 2-stroke engines): How does the engine receive lubrication inside the crankcase if the fuel charge is injected directly into the combustion chamber? I know on a conventional 2S the engine sucks in air/fuel/oil thwough the carburator and reed valve into the crankcase before it heads into the combustion chamber. It lubricates the engine while it whirls around inside before being burned. In a DI 2S, how does oil get to the crankcase? The cartoon drawings on the Nissan website sure make it look like the fuel is squirted in right next to the plug. Clearly, I am missing something obvious here and I don't have any doubts that the system works but am instead curious as to HOW. This is more of a curiousity question than something I really need to know. I have already decided I will be buying a new Nissan 40 hp TLDI in the next month or so since the engines seem impressive and the price is attractive. Hopefully we don't have much ice this winter so I can get it out and run it! Thanks in advance, Steve   Graham Lamb Senior Member Username: galamb Post Number: 2287 Registered: 05-2007 Posted on Wednesday, November 28, 2007 - 02:14 am:    Steve, the Merc and Tohatsu (and Nissan which is just a Tohatsu with different paint/decals) DFI's work almost identical to each other. Here's the jargon from Merc - As the crankshaft rotates, air is drawn into the crankcase through the throttle shutters, into the plenum, and through the reed valves. As the piston nears bottom-dead-center, air from the crankcase is forced through the transfer system into the cylinder. As the crankshaft continues to rotate the exhaust and intake ports close. With these ports closed, fuel can be injected into the cylinder. With the piston in the correct position, the ECM opens the fuel injector, 90 psi fuel is discharged into a machined cavity inside the air chamber of the air/fuel rail. This mixes the fuel with the air charge. Next the direct injector will open, discharging the air/fuel mixture into the combustion chamber. The direct injector directs the mixture at the bowl located in top of the piston. The piston’s bowl directs the air/fuel mixture into the center of the combustion chamber. This air fuel mixture is then ignited by the spark plug. Oil in this engine is not mixed with the fuel before entering the combustion chamber. Oil is stored inside a standard remote oil reservoir. Crankcase pressure will force oil from the remote oil reservoir into the oil storage reservoir on the side of the powerhead. Oil will flow from the oil storage tank into the oil pump. The oil pump is a solenoid design. It is activated by the ECM and includes 7 pistons with corresponding discharge ports. The oil pump is mounted directly onto the powerhead. Each cylinder is lubricated by one of the discharge ports. The oil is discharged into the crankcase. The seventh passage connects to the hose that leads to the air compressor for lubrication. Excess oil from the compressor returns into the plenum and is ingested through the crankcase. Totally confused now?   Steve Member Username: wh500special Post Number: 8 Registered: 09-2006 Posted on Wednesday, November 28, 2007 - 05:06 pm:    Thanks Graham. Actually, I think I get it (although whoever the tech writer for Merc was could have done a better job...). So, the fuel that is injected through the fuel injector is 100% gasoline containing no oil. Oil is "injected" separately by the oil pump into the crankcase where it serves its function and mixes with the incoming air charge where it passively makes its way into the combustion chamber and is burned. excess oil returns to the tank. Pretty elegant design really. I would imagine that since the oil is deposited more or less directly where needed that it takes far less oil to lube the engine than in a conventional 2 stroke where the lubricant is only indirectly sent where needed. Also would explain why during break-in no extra oil need be added to the gas since it would never reach any parts that need it. Seem right? I wonder when the 4S manufacturers will make the next step to direct injection in their designs. Seems like a logical progression to me that would likly get the power:weight ratio in line with 2S engines. Actually, the Verado OB's by Merc would benefit the most by this since they already have a supercharger in place and with DI they could bump up their compression ratios(perhaps they already made the leap...I'm not that familiar with them). Otherwise, I'd bet Honda will get there first since they can "borrow" technology and engineering from the autos. I digress... Thanks, once again, for the assistance! Once I finally "get off the pot" and get my TLDI hung on the transom I'll let you know how I like it. I have decided I am going with a Tiller 40 and Tohatsu tells me the "variable idle" feature is std on both the remote and tiller models...a real plus! Steve   Steve Member Username: wh500special Post Number: 9 Registered: 09-2006 Posted on Wednesday, November 28, 2007 - 05:10 pm:    "excess oil returns to the tank" Strike that. I confused oil returning from the compressor to the intake with my runaway thoughts.   Graham Lamb Senior Member Username: galamb Post Number: 2292 Registered: 05-2007 Posted on Thursday, November 29, 2007 - 11:32 am:    Steve, yes, I think your understanding of what is going on is about the same as mine (and we both could be out to lunch) But yes, no oil on break in, the engine computer controls the amount of oil injected (or pumped) into the powerhead which makes it way more effient and reduces the emissions considerably. The Mercs/Tohatsus/Nissans all use a low pressure direct injector compared with the Evinrude/Yamaha set-ups. In the air/fuel rail on the Mercs, the fuel is at 90psi and the air at 80psi which is then sprayed (injected) through the direct injector - with additional air/oil mix coming from the crankcase. The EV/Yami's use upwards of a 1000 psi to run their injectors.   Tohatsu Guru Member Username: tohatsu_guru Post Number: 46 Registered: 06-2007 Posted on Thursday, November 29, 2007 - 02:23 pm:    Air 79.8 psi...But 80 was real closeTohatsu fuel is at 11.4 psi which is very low.   Tohatsu Guru Member Username: tohatsu_guru Post Number: 47 Registered: 06-2007 Posted on Thursday, November 29, 2007 - 04:34 pm:    Oops. El mistako. 11.4 at the fuel pump and 90 at the injectio point   Graham Lamb Senior Member Username: galamb Post Number: 2293 Registered: 05-2007 Posted on Friday, November 30, 2007 - 12:21 am:    Elvin, isn't is 2 fuel pumps? the one at low pressure (conventional) and then a second electric one to feed the fuel rail (after the vapour separator or as part of it)?? I'm still trying to get a good grip on the way these things function...   Tohatsu Guru Member Username: tohatsu_guru Post Number: 48 Registered: 06-2007 Posted on Friday, November 30, 2007 - 02:42 pm:    It runs from the normal fuel pump(11.4) to the vapor separator. Then it is fed into the high pressure pump(79.8)which feeds it to the rail and then through the injectors.

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