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A major challenge for internal combustion engines (ICEs), and diesel engines, in particular, is the reduction of exhaust emissions, essentially nitrogen oxides (NOx) and particulate matter (PM). In this regard, the potential of LPG-diesel blends was evaluated in this work. The LPG and diesel blends were externally prepared by exploiting their perfect miscibility at high pressures. Two diesel-LPG mixtures with 20% and 35% by mass LPG concentrations were tested. In terms of spatial and temporal evolution, the spray characterization was performed for the two blends and pure diesel fuel through high-speed imaging technique. The combustion behavior, engine performance and exhaust emissions of LPG-diesel blends were evaluated through a test campaign carried out on a single-cylinder diesel engine. Diesel/LPG sprays penetrate less than pure diesel. This behavior results from a lower momentum, surface tension and viscosity, of the blend jets in comparison to diesel which guarantee greater atomization. The addition of LPG to diesel tends to proportionally increase the spray cone angle, due to the stronger turbulent flow interaction caused by, the lower density and low flash-boiling point. Because of improved atomization and mixing during the injection phase, the blends have shown great potential in reducing PM emissions, without affecting engine performance (CO2 emissions). The addition of LPG resulted in a significant smoke reduction (about 95%) with similar NOx emissions and acceptable THC and CO emissions. Furthermore, the low cetane number (CN) and high low-heating value (LHV) ensuring leaner air-fuel mixture, and improvements in terms of efficiency, particularly for a blend with a higher concentration of LPG.

The in-cylinder direct injection of natural gas can be a further step towards cleaner and more efficient internal combustion engines (ICE). However, the injector design and its characterization, both experimentally and by numerical simulation, is challenging because of the complex fluid dynamics related to gas compressibility and the small length scale. In this work, the under-expanded flow of methane from an outward-opening poppet-valve injector has been experimentally characterized by high-speed schlieren imaging. The investigation has been performed at ambient temperature and pressure and different nozzle pressure ratios (NPR) ranging from 10 to 18. The gaseous jet has been characterized in terms of its macroscale parameters. A scaling-law analysis of the results has been performed. The gas-dynamic structure at the nozzle exit has been also investigated

The DI (Direct Injection) in SI (Spark Ignition) engines is rapidly developing and seems very attractive offering the possibility of multi-mode operation, homogeneous and stratified charge, with valuable benefits respect to conventional PFI (Port Fuel Injection). One of the major drawbacks of the GDI-fueled engine is the impingement of liquid fuel on the combustion chamber walls that generally produces an increasing of HC emissions and detrimental effects on the combustion process, like soot formation in the wall guided engines due to the diffusive combustion of fuel film deposits on the piston head. This paper investigates the structure of gasoline spray-wall interaction generated by a single-hole injector for GDI engines in an optically-accessible quiescent vessel. The axially-disposed hole diameter is 0.200 mm with a L/d ratio of 1.0 while the injection pressure and the wall temperature varied in the range of 10.0–20.0 MPa and ambient to 300 °C, respectively. Injection duration of 1.0 ms was investigated and the nozzle tip-wall distance was 22.5 mm. Optical investigations were carried out at atmospheric backpressure by an in-line schlieren optical setup using a LED source while the cycle-resolved images of the evolving impact were captured by a C-Mos high-speed camera with a time resolution of 80 μs and a window size of 640 × 464 pixels. The optic-geometrical setup realized a spatial resolution of 0.039 mm/pixel. The images were treated by a digital processing software for background subtraction and both liquid and vapor contour extractions. The spatial and temporal evolution of the liquid and vapor phases as a function of the wall temperature is described for the different operative conditions.

Gasoline Direct Injection (GDI) is a leading technology for Spark Ignition (SI) engines: control of the injection process is a key to design the engine properly. The aim of this paper is a numerical investigation of the gasoline injection and the resulting development of plumes from an 8-hole Spray G injector into a quiescent chamber. A LES approach has been used to represent with high accuracy the mixing process between the injected fuel and the surrounding mixture. A Lagrangian approach is employed to model the liquid spray. The fuel, considered as a surrogate of gasoline, is the iso-octane which is injected into the high-pressure vessel filled with nitrogen. The numerical results have been compared against experimental data realized in the optical chamber. To reveal the geometry of plumes two different imaging techniques have been used in a quasi-simultaneous mode: Mie-scattering for the liquid phase and schlieren for the gaseous one. Different operating conditions, in terms of temperature and pressure inside the chamber, have been tested to check the robustness of the numerical framework proposed by varying operating conditions. Results obtained show a very good agreement between the numerical results and the experimental data confirming the capabilities of the approach to describe accurately all the physical phenomena involved in the injection process. The influence of the grid size and the number of parcels has been highlighted showing the existence of threshold values for accuracy. Further investigation on the mixing characteristics of the spray have been performed looking at the turbulence generated by the spray-ambient interaction and the local ignition probability index.

The present work is focused on multi-dimensional simulations of combustion in diesel engines. The primary objective was to test, in a diesel engine framework, a soot particle size model to represent the carbon particle formation and calculate the corresponding size distribution function. Simulations are performed by means of a parallel version of the KIVA3V numerical code, modified to adopt detailed kinetics reaction mechanisms. A skeletal reaction scheme for n-heptane autoignition has been extended, to include PAH kinetics and carbonaceous particle formation and consumption rates: the full reaction set is made up of 82 gas species and 50 species accounting for the particles, thus the complete reaction scheme comprises 132 species and 2206 reaction steps. Four different engine operative conditions, varying engine speed and load, are taken into account and experimentally tested on a single cylinder diesel engine fuelling pure n-heptane. Computed particle size distribution functions are compared with corres...

In this article, a glycerol ethers mixture obtained from etherification of glycerol with tert-butyl alcohol and isobutylene has been used in blend (10% and 20% v/v) within a commercial diesel fuel to feed a single-cylinder research engine derived from a Euro5 compliant four-cylinder engine. The engine has been run in three significant operating points in the New European Driving Cycle emission homologation area. The results have shown the possibility to burn the diesel–glycerol ethers mixture blends without significant impact on combustion characteristics and efficiencies while, due to the oxygen content of the glycerol ethers mixture, important benefits are obtained in terms of NOx-particulate matter trade-offs at the exhaust. Moreover, tests have been performed on a diesel engine with optical access through the piston bowl. The injection and combustion processes of the pilot have been investigated by means of the simultaneous use of digital imaging in the visible and infrared ranges in order to have more information on the vapour distribution, the fuel motion before the ignition and the location of hot gas.

Some oxygenated hydrocarbons were tested as pure fuels in two different DI diesel engines, and their emission potential was compared to n-tetradecane combustion. Two colours pyrometry method was used to infer in-cylinder sooting tendency of tested fuels. Pure pyrolysis of the same fuels was also investigated in a conventional shock lube at high temperature (1700–2500 K) and pressure (9–13 bar), using light scattering/extinction methods. All oxygenated compounds tested in the engines exhibited a strong decrease of soot loading compared with tetradecane combustion. The long soot induction times, as measured in shock tube experiments, and the oxygen content of the fuel molecules seem to provide a plausible explanation of soot lacking in oxygenated fuels combustion. Emission measurements at the exhaust of a four cylinder engine fully confirm the trends obtained by two colours pyrometry and shock tube experiments. As a matter of fact, the oxygenated synthetic fuels strongly reduce both gaseous and total partic...

In the present paper, the effect of the clean and cold EGR flow on the performance of a diesel engine running under Low Temperature Combustion conditions is investigated by means of experimental tests on a single-cylinder research engine. The engine layout was “ad hoc” designed to isolate the effect of the clean and cold recirculated gas flow on the combustion quality. The results have shown the possibility to increase the EGR rate by EGR flow temperature reduction, with a decrement of both NOx and PM emissions, at the same fuel consumption, highlighting that the intake manifold temperature is the main factor affecting the engine performances.

The effect of fuel injection strategy and charge dilution on NOx and soot emissions has been investigated with a modern DI diesel engine. Particulate mass has been measured by a standard smoke meter and soot particles have been characterized by means of time-resolved Laser Induced Incandescence (LII) at the exhaust of the engine. Two steady- state test points have been selected, representative of low and medium load conditions. The influence of the different engine management strategies has been assessed, highlighting the potential of unconventional operating modes to meet forthcoming emission limits.