Search Results

It is well known that ethanol can be used in spark-ignition (SI) engines as a pure fuel or blended with gasoline. High enthalpy of vaporization of alcohols can affect air-fuel mixture formation prior to ignition and may form thicker liquid films around the intake valves, on the cylinder wall and piston crown. These liquid films can result in mixture non-homogeneities inside the combustion chamber and hence strongly influence the cyclic variability of early combustion stages. Starting from these considerations, the paper reports an experimental study of the initial phases of the combustion process in a single cylinder SI engine fueled with commercial gasoline and anhydrous ethanol, as well as their blend (50%vol alcohol). The engine was optically accessible and equipped with the cylinder head of a commercial power unit for two-wheel applications, with the same geometrical specifications (bore, stroke, compression ratio).

Polychromatic extinction and chemiluminescence techniques, from ultraviolet to visible, were applied in an optical diesel engine, in order to analyze the temporal and spatial evolution of a high pressure fuel jet interacting with a swirling air motion. A fully flexible Common Rail fuel injection system equipped with a single hole nozzle was used. The experiments were performed at fixed engine speed and air/fuel ratio for three injection strategies. The first one consisted of a main injection to compare with those operating at low pressure injection. The other ones were based on a pilot and main injections, typical of current direct injection diesel engines, with different dwell time. A detailed investigation of the mixture formation process inside the combustion chamber during the ignition delay time was performed. The liquid and vapor fuel distribution in the combustion chamber was obtained analyzing the polychromatic extinction spectra.

Conventional methods to measure gas concentrations and, in particular, NO are typically based on sampling by valve, sample treatment and subsequent analysis. These methods suffer low spatial and temporal resolution. The introduction of high energy lasers in combination with fast detection systems allowed to detect the NO distribution inside optically accessible Diesel engines. In this paper, a high spatial and temporal resolution in-situ technique based on ultraviolet - visible absorption spectroscopy is proposed. The characterization of the combustion process by the detection of gaseous compounds from the start of combustion until the exhaust phase was performed. In particular, this technique allows the simultaneous detection of NO and OH absolute concentrations inside an optically accessible Diesel combustion chamber.

Non-intrusive diagnostic techniques based on broadband (190-550 nm) extinction and scattering spectroscopy were applied at undiluted exhaust Common- Rail (CR) diesel engine in real time. The influence of load and Exhaust Gas Recirculation (EGR) on soot mass concentration, size distribution of emitted particles and NO concentration was analyzed. NO concentration was evaluated by ""in-situ"" ultraviolet-visible absorption measurements and compared with those obtained by conventional analyzer. The extinction and scattering spectra were compared with those evaluated by the Lorenz-Mie model for spherical particles in order to retrieve the size, the number concentration of the emitted particles and particulate mass. The optical measurements showed that new generation diesel engines, in spite of a drastic reduction of the exhaust mass concentration, caused the emission in the atmosphere of high number concentration of carbonaceous nanoparticles.