Why is the compression ratio of gdi engine higher than that of mpi engine?

Port multi-point injection gasoline engine is called MPI in English, and in-cylinder direct injection gasoline engine is called GDI for short. Intake port multi-point injection gasoline engine injects fuel in front of the intake manifold, and then enters the cylinder through the valve. In-cylinder direct injection gasoline engine, as its name implies, injects fuel directly into the cylinder. Firstly, MPI engine injects fuel to the back of the intake valve of each cylinder with the intake valve closed, so that the fuel-air mixture can enter the cylinder during the intake stroke. During cold start, due to incomplete fuel evaporation at this time, oil films and oil pits will be formed on the back of intake port and intake valve, which will make the actually injected fuel amount far exceed the theoretical value, so that there will be obvious misfire or partial combustion in the first 4- 10 cycles of start, which will lead to an obvious increase in HC emissions. GDI is directly injected into the cylinder, avoiding the wet wall of the intake port, and there is no MPI problem, so the HC displacement is not high during cold start, and the second working cycle can operate normally.

Secondly, another limitation of MPI is that the change of load depends on the adjustment of throttle. Although throttle control has developed into a very mature technology for MPI, it brings considerable thermal power loss. Throttle adjustment will produce parasitic pumping loss and reduce the thermal efficiency of the engine at low load. GDI does not need a throttle to adjust the load, thus improving the volumetric efficiency at part load and improving the fuel economy.

In addition, in the aspect of using fuel to cool the charge, the evaporation of MPI fuel mainly depends on the heat transfer from heat sources such as intake port and intake valve to the oil film, so it can not significantly cool the charge; For GDI, the fuel enters the cylinder in the form of fine atomized particles, obtains heat energy from the surrounding air, and effectively cools the charge.

From the above comparison, we can clearly understand that GDI has made great progress in fuel economy and emissions compared with MPI.

In terms of fuel economy, GDI has even surpassed diesel engines and successfully achieved lean combustion of gasoline engines. In terms of power output, GDI is far ahead of MPI.

The evil stick uses GDI itself. The so-called imported goods were changed to MPI to cheat money when they arrived in China, and then changed to GDI to cheat money a year or two later.

In addition, we all know that the horsepower of Yazun GDI is 365,438+00N/m, but it will become 280N/M after changing to MPI, which shows that GDI has greatly improved fuel economy and automobile power compared with MPI.