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The octane appetite of an engine is frequently characterised by the so-called K value. It is usually assumed that K is dependent only on the thermodynamic conditions in the engine when knock occurs. In this work we test this hypothesis: further analysis was conducted on experimental results from SAE 2019-01-0035 in which a matrix of fuels was tested in a single cylinder engine. The fuels consisted of a relatively small number of components, thereby simplifying the analysis of the chemical kinetic proprieties. Through dividing the original fuel matrix into subsets, it was possible to explore the variation of K value with fuel properties. It was found that K value tends to increase slightly with RON. The explanation for this finding is that higher RON leads to advanced ignition timing (i.e. closer to MBT conditions) and advanced ignition timing results in faster combustion because of the higher pressures and temperatures reached in the thermodynamic trajectory.

The temporal and spatial evolution of the ignition and premixed-burn phases of a direct-injection (DI) diesel spray were investigated under quiescent conditions. The diagnostics used included temporally resolved measurements of natural light emission and pressure, and spatially resolved images of natural light emission. Temporally resolved natural light emission measurements were made with a photo-multiplier tube and a photodiode, while the images were acquired with an intensified CCD camera. The experiments were conducted in an optically accessible, constant-volume combustion vessel over a range of ambient gas temperatures and densities: 800-1100 K and 7.3-45.0 kg/m3. The fuel used was a ternary blend of single-component fuels representative of diesel fuel with a cetane number of 45. The fuel was injected with a common-rail injector at high pressure (140 MPa). The results provide new information on the evolution of the two-stage ignition/premixed-burn phases of DI diesel sprays.

Downsized turbocharged gasoline direct injection (TGDI) engines with high specific power and torque can enable reduced fuel consumption in passenger vehicles while maintaining or even improving on the performance of larger naturally aspirated engines. However, high specific torque levels, especially at low speeds, can lead to abnormal combustion phenomena such as knock or Low-Speed Pre-Ignition (LSPI). LSPI, in particular, can limit further downsizing due to resulting and potentially damaging mega-knock events. Herein, we characterize the impacts of lubricant and fuel composition on LSPI frequency in a TGDI engine while specifically exploring the correlation between fuel composition, particulate emissions, and LSPI events. Our research shows that: (1) oil composition has a strong impact on LSPI frequency and that LSPI frequency can be reduced through a carefully focused approach to lubricant formulation.