Reducing vehicle pollution

Dr Fabrizio Bonatesta

Discovering the cause of harmful emissions

Through pioneering investigations into the way soot forms in modern engines, the Engine Modelling Team at Oxford Brookes University is helping automotive manufacturers meet stricter EU regulations aimed at reducing premature deaths due to toxic emissions.

Led by Dr Fabrizio Bonatesta, the team has transformed thinking about engine design at global manufacturer Ford, leading to a fundamental shift in the focus of its planning to meet future emissions targets.

The team’s work has also enabled more accurate digital modelling of engines, allowing software companies to enhance their commercial offering to customers and furthering the growth of digital engineering.

Limiting harmful emissions

Noxious gas dispersion modelling
Noxious gas dispersion modelling

In 2016, the World Health Organisation estimated that more than 4 million people die prematurely each year as a result of being exposed to small particulate matter (PM).

Modern gasoline direct injection (GDI) engines used in road vehicles are a key contributor and particularly harmful, because they produce large numbers of ultra-fine particles that can’t be effectively removed by the tailpipe filters used by most automotive manufacturers. For the GDI engine to remain viable into the future, there was an urgent need to investigate what was causing this, and to develop ways of reducing it.

Soot formation in GDI engines is normally associated with imperfect mixing between air and fuel, and with a liquid film of fuel being deposited on piston and cylinder walls during fuel injection. Fabrizio and his team found that a reduction in piston temperature caused liquid fuel to pool in the combustion chamber. When this liquid was burned (‘pool-fire’), it generated vastly increased emissions. Their findings explained why nano-size particles tended to form in large quantities during engine warm-up and transient operation, such as acceleration.

The team’s work revealed for the first time the full extent to which fuel puddling over the piston crown affects soot generation. Armed with this knowledge, engine designers are able to focus on developing new piston technologies and control approaches to ensure temperatures are maintained throughout all stages of vehicle operation that avoid this liquid build-up.

Ford’s technical expert describes the team’s findings as having ‘completely revolutionised’ the manufacturer’s engine design work.

“[The theory advanced by OBU] was a revelation… For the first time, I could appreciate how… to explain transient PN behaviour […] This new knowledge may assist Ford, and other automotive OEMs, to comply with the increasingly stringent legal PN emission regulations, ensuring the sustainability of GDI engine technology, even in hybrid applications.”

Ford technical expert

Growth of digitalisation

The work of Fabrizio and his team has also made a significant contribution to efforts to accelerate the digitalisation of the automotive industry, improving the accuracy of 3D computational fluid dynamics (CFD) modelling to reduce the industry’s reliance on hardware testing.

The team’s discoveries about how small particulate matter forms in engines enabled them to develop a more accurate GDI engine modelling framework for use by commercial computer-assisted engineering (CAE) software platforms.

As well as new ways to calibrate spray and combustion models, the team proposed a novel methodology for accurate modelling of liquid film formation across a wide range of engine operating conditions.

Their work has already been incorporated into market-leading software released by major industry players Siemens DISW and Ricardo Software. The Siemens DISW software now offers direct calculation of engine charge uniformity, improved numerical stability for modelling liquid film, and improved calculations of PM characteristics.

Further work directly with Ricardo has seen the OBU team develop significantly improved turbulence and combustion models for the company’s 0D/1D WAVE software. A new advanced turbulence model more accurately reflecting the in-cylinder flow characteristics of a modern GDI engine has been integrated into their spark-ignition predictive combustion model as a result.

ICE cylinder computation mesh
ICE cylinder computation mesh

Image credits:

Engine photo by Julian Hochgesang on Unsplash