In this study, processes of a liquid fuel spray ignition and heat release during its combustion were under investigation. The purpose of this study was to elucidate whether the ignition properties and heat release process of a liquid fuel injected into the environments of parameters exceeding its critical values differ from those obtained for subcritical regimes. Therefore, the fuel was injected into the environments of parameters below, around and above its critical values. The ignition and combustion processes were observed by monitoring the pressure in the combustion chamber and by using a high-speed camera through transparent piston. The ignition process was characterized by ignition delay, while the combustion process by heat release and rate of heat release. The ignition delay was determined by pressure rise according to tangential method. Ignition delay determined that way included both physical delay and chemical delay. Obtained results revealed stochastic nature of the spray ignition of n-hexane. No major difference in ignition delay in terms of exceeding critical parameters was noticed. The only parameter directly influencing the ignition delay was the injectant initial temperature.

Searching for further reduction of fuel consumption simultaneously with the reduction of toxic compounds emission new systems for lean-mixture combustion for SI engines are being discussed by many manufacturers. Within the European GasOn-Project (Gas Only Internal Combustion Engines) the two-stage combustion and Turbulent Jet Ignition concept for CNG-fuelled high speed engine has been proposed and thoroughly investigated where the reduction of gas consumption and increasing of engine efficiency together with the reduction of emission, especially CO2 was expected. In the investigated cases the lean-burn combustion process was conducted with selection of the most effective pre-combustion chamber. The experimental investigations have been performed on single-cylinder AVL5804 research engine, which has been modified to SI and CNG fuelling. For the analysis of the thermodynamic, operational and emission indexes very advanced equipment has been applied. Based on the measuring results achieved for different pre-chamber config-urations the extended methodology of polioptimization by pre-chamber selection and the shape of main chamber in the piston crown for proposed combustion system has been described and discussed. The results of the three versions of the optimization methods have been comparatively summarized in conclusions.

The paper discusses the issues of the influence of the fuel spray formation on the generation of self-ignition spots and the development of pre-flame processes in the cylinder of a model diesel engine. The investigations were carried out for a standard diesel fuel and two other types of fuel that were mixtures of ethanol, butanol, and diethylether in a variety of proportions. By applying optical methods of analysis, the authors determined the geometrical indexes of the injected fuel spray as well as fuel mass distribution in the longitudinal and transverse cross section of the fuel spray during the injection process. The location and number of the self-ignition spots in the combustion chamber were evaluated on the basis of a comparison under various conditions: in presence of the charge swirl and at the lack of it. Research conducted for the single-cylinder engine confirmed the possibility of the use of diesel-like fuels for compression ignition engines.

The running diagnostics of the combustion process in an internal combustion engine is essential for increasing its efficiency and to improving its performance indicators. The modern diagnostics of this process no longer concerns only measurements of fast-changing thermodynamic variables, but also measurements of other parameters allowing for its evaluation. The use of electrical or optical methods in diagnostics enables the evaluation of local process parameters, such as occurrence of the flame and its temperature distribution. Actually, there are some new methods under investigation which are proposed for this kind of diagnostic. This article focuses on demonstrating the potential for using an electric signal from the gas ionization to estimate the maximum combustion pressure in a cylinder of an SI engine. This is a comparative analysis of the gas ionization current signal in the cylinder and the fast-changing pressure at fixed operating points of a 4-stroke natural gas powered engine. The study was carried out on a one-cylinder 4-stroke SI engine equipped with a cylinder pressure recording system and monitoring of the cylinder ionization current using appropriate measuring systems. The influence of engine operating conditions on the ability to determine cylinder pressure based on the ionization current signal was analyzed. This impact assessment was analyzed statistically and a strong correlation was found between the analyzed signals. The obtained results point in the potential direction of development of this type of measuring system.