The Gasoline Particulate Filter is on its Way

Huge challenge to designers and calibration engineers – immense time pressure on the development side

From September 2017, new vehicles will be required to meet the EU6c emission standard; one year later, all new cars sold must meet these requirements. For the gasoline engine this means that in Europe, it too will be fitted with a particulate filter. IAV has all the tools as well as the measuring equipment and experience needed to assist its customers in matters of design and calibration. Numerous development projects show that this is highly relevant at the moment.

Under the new standards, gasoline engines in new vehicle types will not be allowed to emit any more than 6 x 1011 particles per kilometer from September 2017. And from September 2018, this ceiling will then apply to all newly sold vehicles – no matter for how long they have been on the market. Although gasoline and the gasoline combustion process produce far less particles than the diesel engines does, EU6c will soon herald in the introduction of particulate filters in gasoline engines too; at least in Europe.

Despite the experience with diesel particulate filters (DPF), gasoline particulate filters (GPF) pose a great challenge for developers. It starts with the package they need. Even today, package downstream of the engine is well filled with numerous components of the exhaust gas aftertreatment system. If the GPF is to be accommodated here as well, the engineers must re-think where to place the other assemblies.

A lot of work is heading towards the calibrators too. Because of its higher exhaust gas backpressure, the GPF affects the engine’s gas exchange and maximum power output. “A particular challenge comes from calibrating the soot models and regeneration strategies, demanding a lot of dynamometer testing”, says Thorsten Stappenbeck, Senior Vice President for Calibration in the Powertrain Mechatronics division. Calibration engineers will only be able to determine the optimum starting point for regeneration with complex load models – this must neither take place too often (unnecessary fuel consumption) nor not often enough (backpressure too high), and there is also a need to consider any temperature peaks that occur.

The sensor system not only needs to identify the state of the GPF on the basis of exhaust gas backpressure, but also has functions of relevance to on-board diagnostics. At the moment, for instance, it must permit installation detection and – with catalytic GPF coating – also provide a catalyst diagnosis.

Joint selection of the best GPF version

The GPF itself is both similar and dissimilar to the DPF. A similarity can be found in the basic structure made up of a ceramic substrate with mutually sealed channels for absorbing particles. New demands are placed on the hardware by the exhaust gas temperatures, which are higher than in the case of the diesel engine, as well as by the lower oxygen content in the exhaust gas. This means that the GPF needs to be thermally robust, with appropriate calibration measures providing a sufficient quantity of O2 for burning the particles.

These days, OEMs can choose from a wide range of GPF variants – including versions with and without coating for the catalyst function or for close-coupled or underbody use. “Here, there’s a matrix of options from which we, together with our customers, can select the best option for the particular engine", says Gerhard Märker, Senior Vice President of Powertrain Integration.

The short timeframe for introducing EU6c is a particular challenge for the engineers needing to develop the new exhaust gas aftertreatment systems for gasoline engine vehicles – not only for new models but also for existing vehicles with neighboring function systems that may be affected by changes in the exhaust gas aftertreatment system. “We have all disciplines under one roof, guaranteeing rapid communication and fast development times”, Stappenbeck says. “We also have all of the tools, test facilities and well-experienced specialists able to assist our clients in all matters of design, calibration, algorithm development and validation.” Many current customer projects show that there is huge demand for GPF expertise.