Quote:
Originally Posted by serialk11r
I don't think you understand what direct injection does. It does not eliminate the throttle.
The most sophisticated variable cam profile systems allow throttle plate elimination at the cost of greater valvetrain power consumption. Honda's R18 and 3-stage VTEC motors allow a rough approximation of this capability, allowing a greater proportion of high throttle position operation.
Even without the throttle restriction, thermal efficiency is still horrible at low load because the combustion temperature and pressures are so low and mechanical efficiency is also low. There is no getting around a combination of downsizing + power adders, shutting the engine off, and using longer gearing.
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Some do it with the valve timing and some just can do it with the direct injection.
From this article, "Some engines with direct gasoline injection do not have a conventional throttle because the throttle is not used to control engine speed and power. The engine computer does that by varying the time and amount of fuel that is injected into each cylinder. Eliminating the throttle means there is no restriction to incoming air and little or no vacuum in the intake manifold. This reduces the normal pumping loses caused by the throttle plates and intake vacuum for improved engine efficiency."
Gasoline Direct Injection
From wiki, " In addition some engines operate on full air intake. That is, there is no air throttle plate eliminating air throttling losses in some GDI engines, when compared to a conventional fuel-injected or carbureted engine, which greatly improves efficiency, and reduces piston 'pumping losses'. Engine speed is controlled by the engine control unit/engine management system (EMS), which regulates fuel injection function and ignition timing, instead of having a throttle plate that restricts the incoming air supply. Adding this function to the EMS requires considerable enhancement of its processing and memory, as direct injection plus the engine speed management must have very precise algorithms for good performance and drivability."
Gasoline direct injection - Wikipedia, the free encyclopedia
These motors I think always still have a throttle body but it's for startup and if something goes wrong with the system.
Diesels have been using direction injection without throttle for a long time with no fancy valve systems. It's their direction injection that made that possible