Reciprocating Compressor 1D Thermofluid Dynamic Simulation: Problems and Comparison with Experimental Data

The authors here extend a 0D-1D thermofluid dynamic simulation approach to describe the phenomena internal to the volumetric machines, reproducing pressure waves' propagation in the ducts. This paper reports the first analysis of these phenomena in a reciprocating compressor. The first part presents a detailed experimental analysis of an open-type reciprocating compressor equipped with internal sensors. The second part describes a 0D-1D thermofluid dynamic simulation of the compressor. Comparison of computed and measured values of discharge mass flow rate shows a good agreement between results for compression ratio < 5 . Then, to improve the model fitting at higher pressures, a new scheme has been developed to predict the blow-by through the ring pack volumes. This model is based on a series of volumes and links which simulate the rings' motions inside the grooves, while the ring dynamics are imposed using data from the literature about blow-by in internal combustion engines. The validation is obtained comparing experimental and computing data of the two cylinder engine blowby. After the validation, a new comparison of mass flow rate on the compressor shows a better fitting of the curves at higher compression ratio

Isolation of Saccharomyces cerevisiae strains from different food matrices and their preliminary selection for a potential use as probiotics

Aims: To isolate acid- and bile-resistant Saccharomyces cerevisiae strains directly from food samples and to preliminarily select them on the basis of fundamental probiotic properties. Methods and Results: A rapid screening method allowed the isolation and selection of 20 acid- and bile-resistant yeasts from foods, avoiding timeconsuming isolation steps. The strains were characterized for their specific survival in simulated gastric juice and in intestinal fluid after pre-exposure at low pH. Ten isolates demonstrated a satisfactory survival percentage in intestinal fluid after pre-exposure to gastric juice and appreciable lipolytic and proteolytic properties, as demonstrated by the API-ZYM test. By using molecular methods five strains were identified as Saccharomyces cerevisiae, three as Candida spp., one as Candida pararugosa and one as Pichia spp. The Saccharomyces cerevisiae strains showed considerable probiotic properties, achieving a 80< % <90 survival through the simulated gastrointestinal tract, as well as interesting glucosidase activities. Conclusions: The research represents an efficient strategy to select and identify Saccharomyces cerevisiae strains with desirable acid and bile resistances. Significance and Impact of the Study: This paper reports the direct selection of potentially probiotic yeasts from foods and provides indications about the ability of Saccharomyces cerevisiae strains to survive conditions simulating the human gastrointestinal tract

Performance and Emissions of a Natural Gas Fueled Two-Stroke SI Engine

ABSTRACT This paper presents the results of an experimental activity carried out on a two-stroke SI engine for moped (with a displacement 50 cm3) fueled alternatively by gasoline and natural gas. The effect of the fuel on engine performance and efficiency was evaluated comparing both instantaneous (pressure signal in the crankcase, cylinder and exhaust pipe) and overall data (torque, power, fuel consumption, emissions). Cylinder pressure was measured in order to evaluate the effect of fuel on the optimum ignition timing angle and on cyclic dispersion. Engine emissions were measured by means of a gas analyzer and a gas-chromatograph. Moreover this experimental analysis has been carried out also to validate the 1D-3D numerical model for the simulation of the scavenging and combustion processes in a small-size spark-ignition two-stroke engine. This activity is reported in another paper

Performance and Emissions of a Natural Gas Fueled Two-Stroke SI Engine

This paper presents the results of an experimental activity carried out on a two-stroke SI engine for moped (with a displacement 50 cm3) fueled alternatively by gasoline and natural gas. The effect of the fuel on engine performance and efficiency was evaluated comparing both instantaneous (pressure signal in the crankcase, cylinder and exhaust pipe) and overall data (torque, power, fuel consumption, emissions). Cylinder pressure was measured in order to evaluate the effect of fuel on the optimum ignition timing angle and on cyclic dispersion. Engine emissions were measured by means of a gas analyzer and a gas-chromatograph. Moreover this experimental analysis has been carried out also to validate the 1D-3D numerical model for the simulation of the scavenging and combustion processes in a small-size spark-ignition two-stroke engine