Laser-induced fluorescence (LIF) for quantitative fuel concentration measurements in a combustion engine is a challenging task. Measuring close to the walls of the combustion chamber is even more challenging as both the incident laser light and the signal are strongly reflected on the walls of the combustion chamber. By using a new technique called Structured Laser Illumination Planar Imaging (SLIPI) such background effects, as well as unwanted multiply scattered light, can be suppressed allowing for higher measurement accuracy. In this article we demonstrate, for the first time, the feasibility of the SLIPI technique for gas phase LIF and in-cylinder measurements. Results from regular LIF and SLIPI measurements are also compared. The measurements were made on a non-reacting fuel-jet with acetone as a fuel tracer in a heavy duty diesel engine (Scania D12). It is observed that the equivalence ratio measured by SLIPI in the free part of the jet is only two thirds of that measured by regular LIF during the early jet development.