Public defence in energy technology, MSc Kristian Rönn

Title of the thesis: Experimental and Modelling Studies on the Impacts of Fuels and Lubricants on Pre-ignition in Spark-ignition Engines

Thesis defender: Kristian Rönn
Opponent: Prof. Bengt Johansson, DTU, Denmark
Custos: Prof. Ossi Kaario,Aalto University School of Engineering

Higher efficiencies are achieved in modern spark-ignition engines through turbocharging. Additionally, internal combustion engines are being developed to utilize renewable fuels, such as green hydrogen. A challenge faced in the development of these engines has emerged in the form of pre-ignition. Pre-ignition occurs as an early ignition of the fuel-air mixture before the spark plug-induced spark. Pre-ignition is a complex problem in spark-ignition engines as it occurs sporadically, its mechanisms are variable, and it can lead to engine failure. The aims of the research were to understand the causes of pre-ignition and find ways to mitigate this issue. Applications of the research include turbocharged gasoline engines for automotive use and industrial-scale hydrogen engines.

This dissertation examined the effects of parameters related to engines, lubricating oils, and fuels on pre-ignition. Key findings of the research include observations on the tendencies of different gasoline compositions to cause pre-ignition. Although high octane numbers indicate low reactivity of a gasoline formulation, they do not guarantee strong resistance to pre-ignition. Experiments and simulations showed that one high-octane fuel formulation was more prone to pre-ignition than several fuels with lower octane numbers. The study revealed that even a high-octane fuel can be susceptible to pre-ignition initiated by hot surfaces in the cylinder. Attempts to reduce the pre-ignition sensitivity of hydrogen by decreasing calcium content in the lubricating oil additive were unsuccessful, contrasting with conclusions found in literature regarding gasoline engine studies. However, the hydrogen pre-ignition experiments showed that alternative base oil formulations in the lubricating oil can reduce the risk of pre-ignition when replacing traditional mineral oils. The research findings can be utilized in the development of fuel and lubricating oil compositions to achieve safer engine operation.

Keywords: Spark-ignition engine, Pre-ignition, Super-knock 

Thesis available for public display 7 days prior to the defence at Aaltodoc. 

Contact information: 
E-mail: kristian.ronn@aalto.fi