C. Bertoli

New findings on combustion behavior of oxygenated synthetic diesel fuels

Abstract New results were obtained on pollutants evolution during the combustion of four oxygenated fuels, whichwere compared with n-tetradecane and n-octane combustion. Three different techniques were adopted on a single cylinder direct injection diesel engine, equipped with optical accesses: two-colour pyrometry for the measurement of in-cylinder soot loading, high speed cinematography for the visualization and analysis of spray and combustion, fast sampling valve for the measurements of in-cylinder combustion products. In particular, the sampling line downstream of the fast sampling valve was adapted for the in-cylinder aldheydes measurements. Heat release analysis and fast sampling valve have shown that CO2 formation rate and heat release rate during the diffusion phase of combustion increase with the fuel oxygen content. Acetylene concentrations are influenced by fuel cetane number and oxygen content but, at the same fuel cetane number, they decrease when oxygen content increases. In-cylinder aldheyd...

A finite conductivity model for diesel spray evaporation computations

Abstract The authors present some spray calculations in a combustion bomb and in a d.i. diesel engine for different test cases varying the formulation of the evaporation model in a modified version of the 3D-fluidynamic KIVA II code. Some numerical tests cases have been performed in a combustion bomb to analyze the influence of the modified evaporation model on droplet heating, evaporation rate and droplet lifetime. The numerical results have been compared with those obtained from the original Spalding model and with some experimental data obtained by an optical technique. In a second set of calculations, the new model has been tested in the combustion chamber of a real d.i. diesel engine. Results in terms of pressure, vapour mass, spray distribution and burned fuel are reported. A preliminary analysis on exhaust emissions has been done.

Experimental Characterization of Combustion Behaviour of New Diesel Fuels for Low Emission Engines

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...

Application of a reduced kinetic model for soot formation and burnout in three-dimensional diesel combustion computations

Using a modified version of the Kiva-2 code, three-dimensional computations of combustion and soot formation were performed, burning tetradecane and n -heptane in a direct injection, naturally aspirated diesel engine. A coupled soot formation and combustion model is proposed. Assuming acetylene as the crucial pyrolitic species, the model takes into acount the fuel-to-acetylene pyrolysis, acetylene oxidation, soot nucleation, and surface growth and soot oxidation. The numerical predictions are compared with the expermental data of heat-release patterns and with the in-cylinder measurements of acetylene concentration and soot volume fraction. C 2 H 2 data were collected using a fast-acting valve, while soot loading was measured with the two-color technique. The improved code is able to predict correctly the combustion and heat-release patterns of the two fuels without any retuning of the model constants. The computational results demonstrate that the reduced kinetic soot model is capable of predicting, with satisfactory accuracy, the local amount of soot and pyrolytic products in the combustion chamber, keeping the main features of the diesel combustion.

Assessment of the Effect of Low Cetane Number Fuels on a Light Duty CI Engine: Preliminary Experimental Characterization in PCCI Operating Condition

The goal of this paper is to acquire insight into the influence of cetane number (CN) and fuel oxygen on overall engine performance in the Premixed Charge Compression Ignition (PCCI) combustion mode.

In-Cylinder Soot and NOx Concentration Measurements in D.I. Diesel Engine Fed by Fuels of Varying Quality

Selected measurements of the in-cylinder soot loading and the gaseous combustion products for ten different innovative fuels, burned in a D.I. diesel engine are presented and discussed. All the fuels which were tested have a very low sulfur content, so the insoluble fraction of the particulate is mainly composed of soot. Two different measure techniques are applied: the two-color pyrometry optical method and the fast sampling of gaseous products in the combustion chamber. A priori and experimental uncertainties relative to the reduction of the data obtained with the two-color measurements are preliminarily investigated. The main results which were obtained are: (a) in pure paraffin fuels the measured soot loading strongly depends upon the cetane number; (b) only in lower (< 58) cetane number fuels the soot loading depends on the aromatic fuel content; (c) tests performed with the fast sampling technique confirm the main trends found when performing measurements with the two-color technique.

Two-Colour Pyrometry Measurements of Soot Loading in a Diesel Engine Burning Model Fuels of Varying Quality

ABSTRACT In the present paper the two-colour technique is applied to study the in-cylinder soot volume fraction evolution in a Direct Injection Diesel engine. A preliminary analysis of the theoretical uncertainty involved in performing the two-colour soot emission measurements is carried out. It is found that, with interference filters at 600 and 1000 nm, and reducing the data with the appropriate numerical algorithm, the total accuracy about soot temperature and volume fraction-values is confined respectively under ± 57 K and ± 30%. The in-cylinder measurements are performed at fixed engine angular speed and injected fuel mass, varying the injection timing and the fuel quality. Employing the two-colour pyrometry technique the following results can be obtained: a) the fuel cetane number controls the soot loading of paraffinic fuels; b) at a fixed level of cetane number (up to 58) the fuel aromatic content strongly influences the engine soot loading amount, but, at a further increase of cetane number (over...

The Influence of Automotive Diesel Back End Volatility and New Fuel Additive Technology on Regulated Emissions

Public concern over diesel emissions and air quality has provided the focus for testing the effects of changes to diesel fuel back end volatility using test fuels obtained by closely following real refinery practice and new fuel additive technology. On a typical European city bus engine, the increase in 95 per cent distillation temperature has no overall effects on regulated emissions; conversely, particulate emissions can be controlled by new fuel additive technology.

The evolution of the diesel combustion system toward the near zero emission goal

In the present paper, a new concept of combustion at low flame temperature, based on the use of highly diluted charge, is presented and its advantages and drawbacks on diesel engine application are critically discussed. In particular, the focus is on the mechanism of soot suppression at a low flame temperature achieved by an adequate use of cooled exhaust gas recirculation (EGR) and injection setting without changing the engine architecture. It was found that the flame temperature limit, corresponding to soot and NOx free conditions, can be achieved at a low load by accurate control of the EGR and injection parameters. Tests have demonstrated that near zero emission limits can be reached in a diesel engine at low load without strong fuel economy penalties. The use of a low temperature super-diluted combustion mode is limited to low load range, indicating that further major research activity is needed to reach reliable practical applications.

Looking at New Concepts for Ultra-Low Emission Diesel Combustion System

The DI (Direct Injection) Diesel engine, which is inherently capable of achieving very low CO2 emissions, is affected by PM (Particulate Matter) that is the typical emission of turbulent diffusion flames and has the drawback of high NOx (nitrogen oxides) emissions. In Europe, the recent progress of diesel technology allows complying, with difficulty, with the EURO IV stage of European light duty vehicles regulation and limits planned for 2008 seem at the moment unachievable without a strong and innovative improvement of the combustion system configuration. In the present paper a new concept of highly diluted and low temperature combustion is presented and analyzed. In particular the mechanism of soot suppression at low flame temperature is achieved by the use of high-rate cooled exhaust gas recirculation. Tests were carried out on a medium duty engine equipped with a mechanical in-line injection pump and two modem common rail prototypes engines.Copyright