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Audi using supplementary port fuel injection to address particulates from gasoline direct injection

Elements of the dual injection system. Red is for the high-pressure direct injection system, blue for the low pressure MPI system. Credit: Audi. Click to enlarge.

The 2.0-liter EA888 Gen3 engine featured in Audi’s all-road shooting brake plug-in hybrid concept unveiled at the North American International Auto Show this week (earlier post) features—as does its production ilk—a dual injection system that combines direct injection with indirect injection into the intake manifold. In part-load operation, the indirect injection supplements direct gasoline injection to improve fuel economy and to reduce the output of particulates from the engine. (Earlier post.)

Audi says the approach is sufficient to meet Euro 6 particle limits without the use of a particulate filter. (Earlier post.) The EU has set a standard for 6 × 1012 number/km limits between 2014 and 2017, tightening to 6 × 1011 number/km. (Earlier post.)

Particle number vs. particle mass for various LDV engine technologies. Source: MECA, Ford Motor Company. Click to enlarge.

GDI technology provides fuel efficiency benefits from charge air cooling, more facile turbocharging, and the downsizing that these permit. The drawback, as noted in a 2013 study by Ford researchers on GDI particulates, is that direct injection of fuel into the combustion cylinder risks liquid fuel impingement onto the piston and cylinder surfaces and inhomogeneous air fuel mixing; consequentially PM formation is higher than in conventional PFI gasoline engines.

A 2012 report on particulates from gasoline vehicles by the European Joint Research Commission found that gasoline direct injection (GDI) vehicles consistently emit a very high number of particles, with the actual emission levels even approaching those of conventional diesels in some cases.

Lean-burn GDI vehicles are generally higher particle emitters than GDIs running on stoichiometric fuel mixtures. Still, the study found, the lowest emitting stoichiometric GDI vehicle exceeded the diesel Euro 5 limit (6×1011 #/km) by more than 100%.

The JRC report noted that it was not clear if OEMs could meet GDI particle limits via engine improvements, or whether this will require the introduction of a Gasoline Particulate Filter (GPF)—a solution that would add to the cost of the already more costly GDI engine itself.

Port Fuel Injection (PFI) engines, on the other hand, have no trouble in meeting the limits, although the number of particles emitted varies with driving behavior.

As described in a paper published in MTZ on the development of the 1.8L TFSI EA888 Gen3 variant, the dual injection system opens up new levels of freedom for engine applications; mixture formation can be carried out by a combination of up to three direct injection events and the indirect injection.

Various assessment criteria are used to co-ordinate the different injection modes, including:

  • efficiency, knocking;
  • emissions, especially particle mass and number;
  • manifold wall condensation, fuel in the engine oil; and
  • smooth running.

The system combines high pressure direct injection and the lower pressure MPI system. The MPI valves are supplied with fuel via a flush connection through the high pressure fuel pump (HPP) in order to guarantee internal cooling of the HPP during MPI operation.

A choke is built into the flush connection to minimize the pulsations transferred to the MPI fuel rail by the HPP. The MPI fuel rail has an integrated low-pressure sensor to regulate the injection volume; the MPI valves are integrated in the Variable Tumble System (VTS) flange.


  • M. Matti Maricq, Joseph J. Szente, Jack Adams, Paul Tennison, and Todd Rumpsa (2013) “Influence of Mileage Accumulation on the Particle Mass and Number Emissions of Two Gasoline Direct Injection Vehicles”, Environmental Science & Technology 47 (20), 11890-11896 doi: 10.1021/es402686z

  • Athanasios Mamakos, Christos Dardiotis, and Giorgio Martini (2012) “Assessment of particle number limits for petrol vehicles” (JRC report)

  • Thomas Heiduk, Michael Kuhn, Maximilian Stichlmeir, Florian Unselt (2011) “The new 1.8L TFSI Engine from Audi part 2: Mixture Formation, Combustion Method and Turbocharging,” MTZ Volume 72, Issue 7-8, pp 58-64 doi: 10.1365/s38313-011-0078-1



Geez, this stuff is getting so complex. We really, REALLY need to fix batteries so we can just drive EVs. LOL


Correcto...but 60+ mpg ICEVs may come before 100+ mpge extended range BEVs bedome common place?


And it can never address the CO2 concerns.EVER!

Nick Lyons

@Arnold: Nuclear-powered synthetic fuel synthesis could keep ICEs going indefinitely with net zero CO2.


This is only a patch that never will fix the problem of PN/PM from GDI engines. It is really a pity that they do not consider using a GPF instead. If the cost is as low as ~40 €, which was suggested in an earlier study (link), there should really be no considerations but to use GPF on all GDI cars in the future. In addition, you can hardly get a second fuel injection system for ~40€. We know from other research that the GPF efficiency can be somewhat lower that the corresponding DPF for diesel cars, but nevertheless, it would provide good filtration at any driving condition not considered by current regulations such as, e.g. full load (fuel enrichment) and cold starts at low ambient temperature. Port fuel injection does not solve the cold start problem at low ambient conditions; it only helps at the ~25°C level considered by current emission regulations. Likewise, the full load problem is not addressed. Optimization (rather than just adopting current DPF technology) could also increase GPF filtration efficiency and the most difficult issue that once had to be solved on diesel cars, filter regeneration, is not an issue for GPFs. GPFs are currently tested by car manufacturers and will be introduced by some manufacturer shortly. When this happen, all the other manufacturers will have to follow, just as what happened in the DPF case. Presumably, however, this will not happen in the USA in a very long time, where US EPA does not consider PM/PN as a health issue. Thus, US citizens will be exposed to high PM/PN levels for the foreseeable future.


But you'd never be able to afford the fuel.  If you're going with nuclear, the cheapest and most efficient scheme is to charge batteries.  Even the 1 kWh/liter iron/molten salt/air batteries would be enough to put 200 kWh aboard a large passenger sedan, making vehicle range limits into an effective non-issue and materials scarcity likewise.


er, 10 kWh/liter.

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