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This work shows the results of an experimental campaign carried out in two spark ignition engines, a small optical research engine and its commercial counterpart, using a turbulent ignition system (pre-chamber) specifically designed for small engines. Advanced optical techniques and conventional methods were used to study the combustion process under various operating conditions. The pre-chamber operated actively in the research engine and passively in the commercial engine. Results showed that the pre-chamber configuration resulted in an increase in indicated mean effective pressure (IMEP) and a decrease in the coefficient of variation (CoV) of IMEP. These improvements compensated for challenges such as slow methane combustion rate, poor lean burn capability, and air displacement. In addition, the pre-chamber configuration exhibited lower fuel consumption and specific exhaust emissions compared to the standard ignition system. The novelty of this work lies in the successful implementation of the turbulent ignition system as a retrofit solution for SI engines, showing improved combustion efficiency and lower emissions. The study goes beyond previous efforts by demonstrating the benefits of the pre-chamber configuration in small engines without requiring extensive modifications. The results provide valuable insights into the automotive industry’s pursuit of engine optimization and highlight the significance of innovative approaches for spark ignition engines in contributing to sustainable mobility.

The investigation of phenomena involved in gasoline direct injection 4-stroke, 4-cylinder, optically-accessible engine were carried out at part load and speed condition with different ethanol-gasoline blends. The influence of injection pressure on ethanol addition, at percentages of 10%, 50% and 85%, was investigated by conventional and optical diagnostics. Combustion characteristics, such as mass fraction burned, heat release rate and combustion duration were calculated based on in-cylinder pressure curve data, Emissions of UHC, NO X , CO, CO 2 , and PM were measured. The injection and combustion phase by high spatial and temporal optical measurements were characterized. The spray penetration, and the flame structure and propagation speed were obtained by optical data. The addition of ethanol in gasoline allowed an improvement of engine performance in terms of IMEP and COVIMEP and emissions. In particular, for E50 the better performance was obtained thanks to an earlier vaporization during the injection and a spray almost compact with a higher penetration especially at 100 bar, that avoided the formation of liquid fuel deposits on the piston and subsequently pollutants in the exhaust. Meanwhile, for E85 the spray was characterized by a slower vaporization that created a less homogeneous charge and reduction of the flame front propagation in the late propagation phase. This allows a faster and more efficient combustion with respect to fuels characterized by high gasoline fraction. Finally, E85 and E50 showed higher values of the integral flame luminosity in the first phase of combustion due to the higher flame speed with respect to gasoline one. Moreover, the chemiluminescence imaging confirmed a lower number of diffusive flames with respect gasoline and E10 in the late combustion phase, when the flame burns the fuel film on the piston crown. These results validated the lower emission of UHC and smoke of E50 and E85 with respect to gasoline and E10.

Various solutions are being proposed and adopted by manufactures and researchers to improve the en- ergetic and environmental performance of internal combustion engines within the transportation sector. For automotive spark ignition engines, gasoline direct injection is one of the presently preferred technolo- gies, in conjunction with turbocharging and downsizing. One of the limiting phenomena of this kind of engines, however, still remains the occurrence of knocking, namely the self-ignition of the so-called end- gas zones of the mixture, not yet reached by the flame front. This phenomenon causes strong in-cylinder pressure oscillations, high stress levels and even damage to engine components. Present work focuses on a numerical and experimental study of a turbocharged GDI engine and is aimed at assessing CFD-O (computational fluid dynamics optimization) procedures to be used in the phase of design as a decision making tool for the development of control strategies for a smooth and efficient operation. A preliminary experimental analysis is performed in order to characterize the con- sidered engine and to investigate the phenomenon of knocking that occurs under some circumstances as the spark advance is increased. The collected data are employed to elaborate a predictive criterion for the appearance of this kind of abnormal combustion, as well as to validate both a 1D and a 3D model for the simulation of the engine working cycle. Various numerical optimization procedures are then realized to increase the engine power output and simultaneously avoid conditions leading to undesired self-ignitions. These are either based on the use of a non-evolutionary algorithm or employ a genetic algorithm in the case multiple contrasting objectives are set. The response surface methodology is also explored as a way to reduce the computational effort.

This work presents experimental tests where lubricant oil was added to the engine in order to highlight its contribution to particle emissions from both gasoline and compressed natural gas spark-ignition engines. Three different ways of feeding the extra lubricant oil and two fuel-injection modes--port fuel injection and direct injection--were investigated to mimic the different ways by which lubricant may reach the combustion chamber. In particular, in the tests using compressed natural gas, the oil was injected either into the intake manifold or directly into the combustion chamber, whereas in both the port-fuel-injection and direct-injection tests using gasoline, the oil was premixed with the fuel. The experiments were performed on a single-cylinder, optically accessible spark-ignition engine, running at 2000 r/min under stoichiometric and full-load conditions, and requiring no lubrication. Particle size distribution functions were measured in the range from 5.6 to 560nm by means of an engine exhaust particle sizer. Particle samples were taken directly from the exhaust flow, just downstream of the valves. Opacity was measured by an AVL 439 opacimeter, and gaseous emissions were measured by means of an exhaust gas analyzer in order to globally monitor the combustion process. Detailed analysis of the recorded total particulate number and particle size distributions allowed to determine the size ranges and relative amounts associated with the lubricant-oil-derived particles. Oil addition produced a significant increase in the particles emitted in the lowest range size, independent of the way lubricant was added. Only when lubricant was injected directly into the combustion chamber (either blended with the fuel or by itself), an increase in the number of particles with sizes larger than 50 nm was recorded

In vehicles fueled with compressed natural gas, a variation in the fuel composition can have non-negligible effects on their performance, as well as on their emissions. The present work aimed to provide more insight on this crucial aspect by performing experiments on a single-cylinder port-fuel injected spark-ignition engine. In particular, methane/propane mixtures were realized to isolate the effects of a variation of the main constituents in natural gas on engine performance and associated pollutant emissions. The propane volume fraction was varied from 10 to 40%. Using an experimental procedure designed and validated to obtain precise real-time mixture fractions to inject directly into the intake manifold. Indicative Mean Effective Pressure, Heat Release Rate and Mass Burned Fraction were used to evaluate the effects on engine performance. Gaseous emissions were measured as well. Particulate Mass, Number and Size Distributions were analyzed with the aim to identify possible correlations existing between fuel composition and soot emissions. Emissions samples were taken from the exhaust flow, just downstream of the valves. Opacity was measured downstream the Three-Way Catalyst. Three different engine speeds were investigated, namely 2000, 3000 and 4000 rpm. Stoichiometric and full load conditions were considered in all tests. The results were compared with pure methane and propane, as well as with natural gas. The results indicated that both performance and emissions were strongly influenced by the variation of the propane content. Increasing the propane fraction favored more complete combustion and increased NO x emissions, due to the higher temperatures. In all tests, natural gas showed the highest PN values. At high speeds, adding propane increased the number of particles between 5 and 30 nm, highlighting the relevance of the ultrafine particles. Smaller differences were recorded at low speeds.