Santiago Molina

A Study of the Relation Between Nozzle Geometry, Internal flow and Sprays Characteristics in Diesel Fuel Injection Systems

This study examines the influence of geometry on the internal flow and macroscopic behavior of the spray in Diesel nozzles. For this investigation, two bi-orifice nozzles were employed : one cylindrical and one conical. The first step is to use a non-destructive characterization method which is based on the production of silicone moulds so that the precise internal geometry of the two nozzles can be measured. At this stage the nozzles have been characterized dimensionally and therefore the internal flow can be studied using CFD calculations. The results gained from this experiment make it possible also to ascertain the critical cavitation conditions. Once the critical cavitation conditions have been identified, the macroscopic parameters of the spray can be studied in both cavitating and non-cavitating conditions using a test rig pressurized with nitrogen and with the help of a image acquisition system and image processing software. Consequently, research can be carried out to determine the influence that cavitation has on macroscopic spray behavior. From the point of view of the spray macroscopic behavior, the main conclusion of the paper is that cavitation leads to an increment of the spray cone angle. On the other hand, from the point of view of the internal flow, the hole outlet velocity increases when cavitation appears. This phenomenon can be explained by the reduction in the cross section of the liquid phase in the outlet section of the hole.

Investigation of the Influence of Injection Rate Shaping on the Spray Characteristics in a Diesel Common Rail System Equipped with a Piston Amplifier

The quality of the mixing process of fuel and air in a direct injection diesel engine relies heavily on the way the spray develops when injected into the combustion chamber. Among other factors, the spray development depends on the injection rate of the fuel delivered by the injector. The paper presents a study, at both a macroscopic and microscopic level, of a Diesel spray generated by a common-rail injection system featuring a piston pressure amplifier. By modifying the timing and the duration of the injector and amplifier piston actuation, it is possible to obtain high injection pressures up to 180 MPa, and different shapes for the injection rate, which would not be achievable with a regular common rail injection system. The spray evolution produced by three different injection rate shapes (square, ramp, and boot) has been investigated in an injection test rig, by means of visualization and PDPA techniques, at different injection conditions. The main conclusions are the important effect on spray penetration of the initial injection rate evolution and the small influence of the maximum injection pressure attained at the end of the injection event. Smaller or even negligible effects have been found on the spray cone angle and on the droplet Sauter mean diameter.

Study of the compression cycle of a reciprocating engine through the polytropic coefficient

The polytropic coefficient during the compression cycle of a reciprocating IC engine depends on the instantaneous values for pressure and volume, as well as on their variations. This dependency makes it useful to solve uncertainties typical of the engine experimental tests, such as the synchronization of pressure and volume signals. Additionally, knowledge of the polytropic coefficient is useful if the heat flux transferred to the walls is to be calculated, this variable being difficult to obtain either from modelling or from measurements, or to minimize errors on the estimation of geometric parameters such as the compression ratio.

Influence of injection conditions and exhaust gas recirculation in a high-speed direct-injection diesel engine operating with a late split injection:

Abstract This paper describes an investigation on low-temperature combustion in a small single-cylinder high-speed direct-injection diesel engine. This engine is representative of turbocharged passenger car diesel engines equipped with a particulate trap and an oxidation catalyst. A medium-load engine operation condition was evaluated using two fuel injection events near top dead centre and high levels of exhaust gas recirculation. The combustion was characterized by extremely low emission of nitrogen oxides (of the order of 10—15ppm) and low combustion noise. The study was carried out by means of a design of experiments, consisting of four factors varied on three levels according to a Box—Behnken design. This Box—Behnken design was extended with validation points, allowing all factors to be studied independently in a parametric approach. Additionally, some relevant two-factor interactions have been studied. The investigated factors were the exhaust gas recirculation rate, the combustion phasing, the injection pressure, and the dwell between the split injections. The results show how it is possible to achieve very low levels of nitrogen oxides and low combustion noise with reasonable fuel consumption, smoke emissions, hydrocarbons, and carbon monoxide emissions, with injection and combustion just after top dead centre.

The effect of swirl on combustion and exhaust emissions in heavy-duty diesel engines

Abstract The effect of in-cylinder air swirl on diesel combustion and exhaust emissions has been studied in a heavy-duty diesel engine. A 1.8 L single-cylinder diesel engine fitted with a device to modify the swirl rate was used. This device allowed variation of the mean swirl ratio, a parameter related to the ratio of the angular velocity of the air within the combustion chamber and crankshaft angular rotation, from 0 to 5.33. Although no single optimum swirl level has been found, the results presented here give an insight into swirl effects on diesel engine combustion and exhaust emissions over a wide range of engine operating conditions.

Methodology for measuring exhaust aerosol size distributions using an engine test under transient operating conditions

A study on the sources of variability in the measurement of particle size distribution using a two-stage dilution system and an engine exhaust particle sizer was conducted to obtain a comprehensive and repeatable methodology that can be used to measure the particle size distribution of aerosols emitted by a light-duty diesel engine under transient operating conditions. The paper includes three experimental phases: an experimental validation of the measurement method; an evaluation of the influence of sampling factors, such as dilution system pre-conditioning; and a study of the effects of the dilution conditions, such as the dilution ratio and the dilution air temperature. An examination of the type and degree of influence of each studied factor is presented, recommendations for reducing variability are given and critical parameter values are identified to develop a highly reliable measurement methodology that could be applied to further studies on the effect of engine operating parameters on exhaust particle size distributions.

Influence of Boost Pressure and Injection Pressure on Combustion Process and Exhaust Emissions in a HD Diesel Engine

The scope of this study is the analysis of the influence of boost pressure and injection pressure on combustion process and pollutant emissions. The influence of these parameters is investigated for different engine speeds. Fuel mass was kept constant for all the tests in order to avoid its influence on the analysis. A single cylinder research diesel engine, equipped with a common rail injection system capable of operating up to a maximum pressure of 150 MPa was used. Special attention was paid to NOx, smoke (which are the most important pollutants for legislation) and brake specific fuel consumption.

The use of micro-orifice nozzles and swirl in a small HSDI engine operating at a late split-injection LTC regime

Abstract This paper describes the investigation of low-temperature combustion (LTC) in a small single-cylinder research high-speed direct injection (HSDI) diesel engine. This engine is representative of passenger car turbocharged diesel engines equipped with a particulate trap and an oxidation catalyst. A medium-load operation mode has been evaluated where the diesel fuel is injected in two injection events close to top dead centre, and high levels of exhaust gas recirculation are used (near stoichiometric air-fuel ratios). The combustion is characterized by extremely low emission of nitrogen oxides (of the order of 10–15 parts per million) and low combustion noise. Three injector nozzles have been tested with 6, 12, and 18 orifices. The orifice diameters are in the range 70–120 μM and have been chosen to obtain injector nozzles with the same hydraulic flow. All three nozzles have been tested at a condition without swirl and at a mean swirl number of 1.7. The effects of the nozzle orifice number and swirl have been investigated by means of analysis of fuel spray, combustion, and emissions. It was found that when the number of orifices is increased, the rate of heat release during the first half of combustion is enhanced. However, during the second part of the combustion, interactions between sprays worsen the air-fuel mixing process and reduce the rate of heat release. Swirl was found to amplify the effects of spray interactions. While normally swirl speeds up the combustion in the second half of the combustion, the opposite happens when spray-spray interaction occurs.

Influence of injection rate shaping on combustion and emissions for a medium duty diesel engine

This paper describes the effects of injection rate shaping on the combustion, fuel consumption and emission of NOX and soot of a medium duty diesel engine. The focus is on the influence of four different injection rate shapes; square type 1, square type 2, boot and ramp, with a variation of maximum injection pressure and start of injection (SOI). The experiments were carried out on a 1 liter single cylinder research diesel engine equipped with an amplifier-piston common rail injection system, allowing the adjustment of the injection pressure during the injection event and thus injection rate as desired. Two strategies to maintain the injected fuel mass constant were followed. One where rate shaping is applied at constant injection duration with different peak injection pressure and one strategy where rate shaping is applied at a constant peak injection pressure, but with variable injection duration. Injection rate shaping was found to have a large effect on the premixed and diffusion combustion, a significant influence on NOx emissions and depending on the followed strategy, moderate or no influence on soot emission. Only small effects on indicated fuel consumption were found.

Multi-objective optimization of heavy duty diesel engines under stationary conditions

Abstract New technological developments are helping to control contaminants in diesel engines but, as new degrees of freedom become available, the assessment of optimal values that combine to reduce different emissions has become a difficult task. This paper studies the feasibility of using artificial neural networks (ANNs) as models to be integrated in the optimization of diesel engine settings, with the objective of complying with the increasingly stringent emission regulations while also keeping, or even reducing, the fuel consumption. A large database of stationary engine tests covering a wide range of experimental conditions was used for the development of the ANN models. The optimization was developed within the frame of the European legislation for heavy duty diesel engines. Experimental validation of the optimized results was carried out and compared with the ANN predictions, showing a high level of accuracy, especially for fuel consumption and nitrogen oxides (NOx).