Yes, because of the combination of positive effects of both systems, it is used in sport- and racing-engines. Port injection gives the possibility to increase volumetric efficiency due to cooling down intake air. In addition, it shows advantageous in the mixture preparation process. For this purpose, port injection nozzle is placed in front of the intake funnel in the air box (in racing and sport cars / motorcycle engines). Direct injection has advantages in view of knocking behavior, volumetric efficiency and in supercharged engine concepts. A combination of both can increase maximum power output and torque behavior of the engine.

In standard automotive applications, the motivation of direct injection is mainly driven by reduction of fuel consumption. In this case, the advantages of a combination are restricted.

Kind regards,

Mario

Yes it has been used and is still in use: there was a Lexus GS450h in 2005. There is also some works in order to be able to cope with dual fuel system. The most recent interest seems to be to lower the particle count down to below Euro 6 standard without selective after-treatment: Audi uses it on a recent 4 cylinder 2.0 liter engine following the 1.8l from 2011.

Regards

One example I know of is the recent Ultraboost engine which utilizes the same injection method. The work among others was published in the 21st Aachen Colloquium proceedings and in the SAE Int. Engine. Hope this helps.

Engines with both direct injection and port fuel injection already exist in serial production. I have two examples in mind :

- The first one is an engine produced by Toyota, the 2GR-FSE, that was launched in 2005.

- More recently, Audi has adopted this technology on its 1.8L and 2.0L TSI gasoline engines.

The bi-injection allows to use the best system at each operating condition :

- At high speed, high load, the direct injection and its related cooling effect delays the knock event.

- At low speed, the PFI gives more time to make the mixture homogeneous, and so reduces unburnt hydrocarbons, carbone monoxide and soot particles while increasing the efficiency.

Thank you for your answers, they really help me a lot. Where do you get these information? Could you recommend me some websites or some related resourses?

As already stated, it's about combining the advantages of each system. Thus, many control strategies are possible... You can understand more by reading the files attached (written in French, as they are downloaded from a French website which I highly recommend (http://www.auto-innovations.com/).

To Adrian Clenci

Thank you very much for your kind help.

Use of combined GDI/PFI systems reduces PM emissions from GDI to essentially the same level as PFI.  The PFI system can be used for cold start and initial warm-up, reducing surface impingement and also allowing direct-injection to be avoided when the piston crown is still cold.

To Joseph F McDonald

Thank you for your answer. PFI is adopted to cold start, does it become hard to ignite the fuel gas? Because of the spark ignition, is it easier for gasoline engine to be ignited at low temperature or lean fuel conditions than diesel engine?

Thank you vergy much!

There advantages and disadvantages to both GDI and PFI for cold start.  Newer versions of GDI with 250-bar or higher injection pressures can attain very good fuel atomization during cold start and can achieve closed-loop operation very quickly.  Fueling and spark timing strategies for GDI to achieve the fast catalyst light-off necessary to meet U.S. NMOG and NOx standards sometimes results in elevated PM emissions.  Also, fuel impingement onto a cold piston crown and diffusion combustion off of the top of the piston crown (pool fires) result in high PM emissions until the piston reaches normal operating temperatures.  Accomplishing catalyst heating and piston warm-up using PFI or combined PFI/GDI operation can lower PM emissions significantly while maintaining low NMOG and NOx emissions.

There is not much point using PFI combined with DI in Spark Ignited Engine much. Let's call it for all-purpose as GDI now. PFI doesn't guarantee fuel vaporization in the manifold, in some literature provided evidence of using the hot spot in the manifold, to target fuel for instant vaporization in the manifold.

Using DI induction allows charge cooling, improving the volumetric efficiency of the engine. Problems do arise in case of cold start, where you can utilize negative valve overlap to trap residual in early exhaust stroke using optimization of exhaust valve timing.

A: Early Exhaust Valve Open (EEVO) minimizes expansion ratio, resulting in the high-temperature exhaust, that might be used for after-treatment using catalyst as they need optimum temperature.

B: Early Exhaust Valve Close (EEVC) maximizes trapped gases and further leads to their compression by the piston in the exhaust stroke, which could be used to accelerate the vaporization of fuel, thereby minimizes piston and wall film formation.

C: There is evidence in the literature for the utilization of backpressure using the valve in the exhaust outlet to increase backpressure, which increases the pumping work of the engine, so in order to maintain power output, the engine is pushed to burn more air and fuel, which in turn increase the exhaust flow rate. This strategy involves late exhaust valve closing (LEVC)

Strategy 1: Combine A and C to promote exhaust after-treatment by the catalyst using EEVO and LEVC, together they provide a high enthalpy exhaust flow rate.

Strategy 2: Combine A and C, lower expansion ratio increases exhaust temperature, combine with compression in the exhaust stroke, i.e. EEVO and EEVC to maximize trapping due to negative overlap, combine with high temperature, causes instant vaporization during the cold start to minimize wall and piston film formation.

There might be a problem with strategy 2 of the backflow of trapped gas since they are compressed at high pressure during exhaust, that why we open exhaust valve (EVO) midway in exhaust stroke for normal timing to limit the pressure of exhaust gas at TDC. This strategy will be accompanied by a late intake valve open (LIVO), to limit backflow.

Reference: Heywood Chapter 6: Gas Exchange Process, section after the choke flow intake equation (Eq: 6.9).

And there are other reasons why PFI is now bad:

1: Injection duration is limited by the intake valve opening duration. As it is carried by intake flow in the cylinder.

2: We can't practice new modern combustion strategies like flash boiling, valve deactivation (case of multi-valve engine), skip fire or rolling cylinder deactivation.

I strongly disagree, Mr. Singh. Combined PFI/GDI fuel systems have been in the North American market since 2007. Every Toyota product using GDI that has been introduced to the North American market over the past decade also has a PFI system, and thus has a combined PFI/GDI fuel system. All recently introduced Ford GDI engines for light truck applications also include a PFI system. In some cases, PFI is being added to GDI engine designs in order to meet U.S. Tier 3 PM emissions standards and/or to prepare for the full phase-in of the more stringent LEV III PM emissions standards in California and some other regions of the U.S. Such systems are also being introduced as lower-cost alternative to the use of GPFs to meet EU Stage 6 light-duty PN emissions standards.

Keep in mind that modern, combined PFI/GDI systems have independent control, and thus are not necessarily used simultaneously. GDI can be used for an initial "lean start" mode, then quickly transitioned to PFI to prevent piston-wetting and "pool fire" formation of PM during the initial catalyst warmup after cold startup. A combination of GDI and PFI can also be used during high-speed, high load operation. GDI-only can be used at large throttle openings and low speeds to better mitigate pre-ignition. Combining the two systems also reduces carbon deposit buildup on the intake valves.

Yes, Joseph, I agree with your analysis, PM/PN is primarily limiting GDI application. But, we can't just overlook the gain in fuel consumption that arise achieved for GDI operation. There is research going on for use of oxygenated fuel blend for GDI, but research is unconfirmed.

There is research that is based on injection timing, pressure, and duration solely on GDI based operations that are producing good results in some steady cases.

When it comes to drive-cycle we have a problem. My point is PFI will be out of the picture in the next few decades, or at least load range application will be limited like you have pointed out combined PFI/GDI operation.

I'm not sure I understand your response. The improvement in fuel consumption from GDI as a knock mitigation measure is also true of a combined GDI/PFI system since it does have a complete GDI fuel system in addition to PFI. The combined GDI/PFI systems used by Ford and Toyota maintain comparable compression ratios to competing GDI-only systems. EPA benchmarking of the Toyota Toyota A25A-FKS engine with Atkinson Cycle, cooled EGR, and a dual GDI/PFI system demonstrated perhaps the highest reported brake-thermal-energy of any spark-ignited engine used outside of HEV applications, with 41% BTE at peak (Kargul, J., Stuhldreher, M., Barba, D., Schenk, C. et al., “Benchmarking a 2018 Toyota Camry 2.5-Liter Atkinson Cycle Enginewith Cooled-EGR,” SAE Technical Paper 2019-01-0249, 2019, doi:10.4271/2019-01-0249 - attached).

Yaopeng Li PFDI technology gives benefits of both Direct and port fuel injections. Ability to hold knock borderline higher by in-cylinder charge cooling (allows higher CR) and eliminating the PM formation due to fuel rich spots. In addition PFDI gives us the ability to flow more EGR because of increased combustion stability in low/mid loads. In one sentence PFDI allows low speed high load engine operation which is very crucial for Fuel Economy with extra EGR.

I totally agree with reply of @ Joseph F McDonald