{"id":20357,"date":"2020-10-22T11:09:41","date_gmt":"2020-10-22T15:09:41","guid":{"rendered":"https:\/\/blogs.sw.siemens.com\/simcenter\/?p=20357"},"modified":"2026-03-26T06:19:49","modified_gmt":"2026-03-26T10:19:49","slug":"liquid-film-adding-realism-to-in-cylinder-simulations-in-simcenter-star-ccm","status":"publish","type":"post","link":"https:\/\/blogs.sw.siemens.com\/simcenter\/liquid-film-adding-realism-to-in-cylinder-simulations-in-simcenter-star-ccm\/","title":{"rendered":"Liquid film \u2013 Adding Realism to in-cylinder CFD simulations"},"content":{"rendered":"\n

2020 will go down in history as a record-breaking year. Personally, I was looking forward to seeing a few records being broken at the 2020 Summer Olympics in Tokyo<\/a>. I was desperately waiting for Team GB improving on its record breaking haul of 63 medals from Rio 2016<\/a>. Unfortunately, this event, like many others, was cancelled as the world was gripped by the COVID-19 pandemic.  In the constant stream of news broadcasts and articles during the lockdown, there was one story that I found particularly interesting. It was about the record fall in air pollution in major cities around the world. Here in the UK during lockdown, car journeys at one point fell by 50-60%<\/a>. This, together with a reduction in industrial activity, brought about significant reductions in the emission of small Particulate Matter (PM). <\/p>\n\n\n\n

\"ParticuleMatter\"
Source: BBC News article – Coronavirus: Lockdown prompts clear fall in UK air pollution<\/a>  <\/figcaption><\/figure><\/div>\n\n\n\n

As lockdown measures were gradually lifted, economic activity and car usage increased. So these improvements in air quality will probably be short-lived as emissions levels are expected to return to normal.<\/p>\n\n\n\n

The ICE age is not over, but only simulation will save it from melting away<\/h2>\n\n\n\n

Undoubtedly the move toward vehicle electrification will bring about reductions in local emissions and improvements to air quality. But nevertheless, recent research suggests that the internal combustion engine (ICE) will still be around for quite a few more years to come. The graph below highlights that ICE will be accounting for up to 76% of all new car sales in 2030 and 46% of all new car sales in 2040.<\/p>\n\n\n\n

\"BNEF
Source: Bloomberg New Energy Finance<\/figcaption><\/figure><\/div>\n\n\n\n

If the forecasts are true, that\u2019s a lot of engines that need to be produced! However, automotive manufacturers face some serious challenges in the coming years. ICE solutions will need to satisfy increasingly stringent regulations linked to improvements in fuel consumption and lower emissions. Coupled to this, manufacturers will need to focus on keeping development costs and design cycle times low. Investing in simulation solutions is key to meeting these challenges.<\/p>\n\n\n\n

Liquid film matters<\/h2>\n\n\n\n

Spray-wall interaction and the resulting \ufb01lm dynamics are a topic of significant interest to ICE practitioners. It is well known they have a substantial effect on engine performance and emission control. It is essential for the injected fuel to suf\ufb01ciently vaporize and mix with the intake air. One, in order to achieve ef\ufb01cient combustion and, two for optimum power generation. However, this is far from straightforward to achieve in the challenging environment of an internal combustion engine.<\/p>\n\n\n\n

Liquid film in Gasoline Direct Injection<\/h3>\n\n\n\n

Take gasoline direct injection gasoline engines, or GDI engines as they are more commonly known. Here fuel is injected directly into the combustion chamber. Liquid films can be generated by impingement of fuel spray onto the piston crown. If there is not sufficient evaporation, small pools of liquid fuel can form on the piston crown. Those may ignite during combustion to create so called \u201cpool fires\u201d. This can have potentially detrimental consequences since such events are known to generate Particulate Matter (PM) emissions. Impingement of the fuel spray onto the piston crown and formation of liquid films is highlighted by the following CFD simulation.<\/p>\n\n\n\n

Port fuel injection – liquid film for a living<\/h3>\n\n\n\n

In the case of port fuel injection engines (PFI), the fuel is injected in the intake port. In most modern designs it impinges on the intake valves, see the animation below.<\/p>\n\n\n\n