Laser ignition was used to operate a four-stroke, four-cylinder, multipoint fuel injection gasoline passenger car engine, replacing the engine classical ignition device. The laser ignition system was compactly built with diode end-pumped Nd:YAG/Cr⁴⁺:YAG composite ceramics, each laser spark plug delivering pulses at 1.06 μm with 4 mJ energy and 0.8 ns duration at variable repetition rate, in accordance with the engine speed. The engine was operated at constant speed–constant load condition of 2000 rpm–2 bar equivalent brake mean effective pressure, and different ignition timings, thus simulating city traffic situations. Two relative air-fuel ratios have been considered: λ~1 for the stoichiometric mixture operation and λ~1.25 for the lean mixture condition. Parameters indicating engine performance, efficiency, combustion stability, and emissions have been measured and registered when groups of 500 consecutive cycles were acquired. The engine brake power, brake specific fuel consumption, coefficient of variability for indicated mean effective pressure, initial and main combustion stage durations, as well as exhaust emissions like carbon monoxide (CO) and total unburned hydrocarbons (THC) emphasized that significant improvements can be obtained for lean air-fuel mixture operation. Increases of the nitrogen oxides emission (NO_x) were measured when laser ignition was used.

The impact of fossil fuel utilisation in different combustion systems on climate change due to greenhouse gas accumulation in the atmosphere is rather evident. A part of these gases comes from the large engines used for propulsion in marine applications. In the continuous global effort made by engine manufacturers to mitigate this negative impact, one way is represented by the utilisation of alternative fuels such as biodiesel and methanol, based on dedicated research to fulfil the more stringent regulations concerning pollutant emissions issued by piston heat engines. In this study, a numerical investigation was conducted on a four-stroke large marine diesel engine (ALCO 16V 251C) at several engine speeds and full load conditions. Different blends of diesel–methanol and biodiesel B20–methanol with methanol mass fractions of 10% and 20% were considered for theoretical analysis in two techniques of methanol supply: direct injection mode of a blend of base fuel diesel/biodiesel B20 with methanol and injection of methanol after the intercooler, and direct injection of the base fuel. The results show that, if 10% in power loss can be acceptable, then for diesel–methanol 10%, in the direct injection technology, the NOx emission can be reduced up to 19%, but with a compromise of an 8% increase in SOOT emission, while for biodiesel B20–methanol 10%, with the same direct injection method, the NOx emissions increase by up to 58% with the benefit of reducing SOOT by up to 23% relative to the original diesel fuel operation. For a 20% methanol fraction in blend fuel, the drop in power is more than 10% regardless of the method of methanol supply and the base fuel, diesel, or B20 used.

The marine sector represents probably the most powerful segment of international transport. Most ships use diesel engines for propulsion. Pollutant emission regulations with their continuous decline of acceptable limits put huge pressure on engine manufacturers. The use of low-quality fuels makes the marine sector a significant contributor to global pollution. The present study shows how turbocharger operating parameters and replacing diesel fuel with biodiesel B20 (20% oil and 80% diesel volumetric fractions) affect the performance, efficiency and pollutant emissions of a four-stroke diesel engine ALCO V16 251F for marine application. A combustion model developed with the AVL BOOST software was used to perform calculations using diesel fuel and biodiesel B20 for different turbocharger characteristics and injection timings. The model was calibrated against experimental data measured on a tested engine at the application site using diesel fuel and operating in a stationary condition of full load at 600, 700 and 800 rpm engine speeds. The results show that the cumulative effects of using an improved turbocharger associated with B20 fuelling under optimized injection timings could provide reductions of 45% for soot and 5% for NO_x, while maintaining the same engine performance obtained with diesel fuel operation.

The combustion process in diesel engines is controlled by the injection rate shape. The stricter emission regulations requiring simultaneous reduction of nitrogen oxides and particulate matter imposes intense research and development activity for achieving clean and robust combustion. This work describes the experimental investigation made for calibration of an engine model and the numerical investigation performed to assess the influences of different injection rate shapes on performances of a diesel engine fuelled with diesel and rapeseed biodiesel B20. The engine model was developed with the AVL-BOOST code using the AVL-MCC combustion mode. The model was calibrated for the reference Top-Hat injection rate shape using experimental data registered for maximum brake torque and maximum brake power speed conditions. Other injection rate shapes such as triangular, trapezoidal, and boot having the same area, start, and duration of injection were investigated in terms of combustion characteristics, performance, and pollutant emissions. The link existing between the injection characteristics and the NO_x and Soot emissions highlights that, for the optimal rate of injection shape, a simultaneous reduction of NO_x and Soot by 11%, respectively 4% for maximum brake torque and by 22%, respectively 7% for maximum brake power, can be obtained using biodiesel B20.

Out of the alternative fuels for spark ignition (SI) engines, natural gas (NG) is one of the best substitutes for gasoline. To show the full ecologic potential of NG, based on a current turbocharged diesel engine, a so-called “monovalent” SI engine was developed at the University of Pitești. In other words, to properly make use of the NG high-octane number, the prototype engine features an 18.25 compression ratio. Therefore, the compromise usually made to allow the SI engine to run in bi-fuel mode (either fueled with gasoline or with NG) is not present in this case. This being the context, the paper presents experimental results obtained at the engine test bench when using NG. As it is a highly compressed SI engine, gasoline could not be used because of the knocking issues. So, to be able to perform a comparison of the NG effects, liquified petroleum gas (LPG) was also used. The operating point used is 2000 rpm and 2 bar of BMEP. Since during engine testing, the exhaust gas analysis was not available, to obtain information about the chemical species that resulted while burning NG and LPG, a 1D model was developed in AVL Boost, which was calibrated and validated based on the available experimental data issued from the test bed. Thus, this paper presents an analysis of the engine-out emissions while using NG and LPG, showing a significant decrease in NO_x and HC for the NG case.

This study investigates the effect of ambient conditions, particularly the humidity of the intake air, on the operation of an ALCO V16 251F (USA) diesel engine. It evaluates the temperature at which air is delivered to the combustion chamber, after the cooling process is accomplished within the aftercooler heat exchanger. A theoretical analysis was conducted using AVL CRUISE software, a specialized computational tool developed by AVL that facilitates the simulation and virtual integration of engine subsystems. An experimental investigation on the operation of air coolers is difficult to perform on a test bench, due to the overall dimensions of heat exchangers used in large marine diesel engines. The simulation results show that the AVL CRUISE virtual cooler reproduces the temperature range of the ALCO aftercooler with small deviations of approximately 7% at the fluid outlets. In these conditions, simulation outcomes demonstrate that the engine’s original charge-air cooler can maintain a stable and controlled air temperature at the intake manifold inlet. For an absolute air humidity of 5%, only minor variations (less than 1%) were registered in the outlet air temperature from the aftercooler, accompanied by 0.7% decrease in cooling effectiveness and 0.6% decrease in heat-exchanger efficiency. These findings confirm that the charge-air cooler operates reliably under humid marine conditions and that the virtual model is suitable for further optimization studies.