Nucleation at high pressure II: Wave tube data and analysis.

Nucleation rate data, obtained from expansion wave tube experiments, are reported for several vapor–gas mixtures at high pressure. Results are given for water–vapor in the presence of helium and nitrogen gas, and for n-nonane in helium and methane. For all these mixtures, carrier gas pressures of 10, 25, and 40 bar have been applied, with temperatures ranging from 230 to 250 K. An extended form of the nucleation theorem (in terms of the derivative of the nucleation rate with respect to carrier gas pressure) is derived, which appears to be very helpful in the interpretation of high pressure data. It can be used to obtain the carrier gas content of the critical nucleus directly from the pressure dependence of experimental nucleation rates. Combining this method with the theoretical considerations of part I of this paper [J. Chem. Phys. 111, 8524 (1999), preceding paper]: the nucleation behavior of water at high pressures of both helium and nitrogen can quantitatively be understood. For n-nonane in helium our "pressure perturbation approach" is also valid. For n-nonane in methane, however, this approach fails because of the high methane solubility in the liquid phase

Homogeneous nucleation rates for n-pentanol from expansion wave tube experiments

Within the scope of joint experiments by the international Nucleation Workshop Group, nucleation experiments on n-pentanol were carried out using a pulse-expansion wave tube. Data were obtained for nucleation at temperatures between 240 K and 260 K. Total pressures of the carrier gas (helium) during nucleation varied from 89 to 109 kPa. The results are presented in tabular form, to facilitate future comparison. Our results are consistent with existing data by Hrubý et al. Comparisons are made to the Kinetic Classical Theory (KCT) as well as to the semiphenomenological theory by Kalikmanov and Van Dongen (KvD–SPT). Although both theories predict nucleation rates that are apparently too low in the temperature range of interest, the KvD–SPT is approximately two orders of magnitude closer to the experimental result

Experimental study on the impact of operating conditions on PCCI combustion

In a short–term scenario, using near–standard components and conventional fuels, PCCI combustion relies on a smart choice of operating conditions. Here, the effects of operating conditions on ignition delay, available mixing time, combustion phasing and emissions are investigated. In the PCCI regime, NOX and smoke have been shown to be efficiently reduced with elongated mixing time. For viable PCCI combustion, one would require a Combustion Delay (CD) which is long enough to bring both NOX and smoke levels down to acceptable values. For the completeness of combustion, the resulting unburned hydrocarbon and carbon monoxide emissions, as well as the associated fuel consumption; mixing time should, however, be as short as possible. Most parameters strongly correlate with combustion delay, independent of how this is achieved. Lastly, the best points experienced for a number of cases are given

Fuel formulation and mixing strategy for rate of heat release control with PCCI combustion

Premixed charge compression ignition (or PCCI) is a new combustion concept that promises very low emissions of nitrogen oxides and of particulate matter by internal combustion engines. In the PCCIcombustion mode fuel, products from previous combustion events and air are mixed and compresseduntil the resulting mixture locally auto-ignites. Auto-ignition at other places in the reacting mixture follows rapidly and combustion takes places across the combustion chamber within a short period. A majorchallenge with PCCI combustion is the accurate control of the start of combustion and of the rate of heatrelease during combustion

Spray growth of regular, synthetic, oxygenated and biodiesels in an optical engine

Spray formation has been studied in an optically accessible heavy-duty diesel engine for regular diesel,synthetic, oxygenated and biofuels using a high-speed digital camera. Images are analyzed with custom madealgorithms to obtain spray penetration length and spray cone angle as function of time. Results from 2 out of the 8 nozzle sprays have been used in the data analysis. Variation in spray equilibrium length and angle is observed between the fuels tested. Modelling of the fuel injection, taking great care to account for individual fuel properties, shows good correspondence with experimental results

Spray combustion in engines

A few lecture hours and some pages of lecture notes are by far not sufficient to cover the broad subject of spray combustion in engines. As a matter of fact, dedicated journals and books exist on sprays. Therefore, the current lecture only serves as an introduction to the subject. Optimally, the lecture slides, text and references in this chapter should function as a "Quick Start Guide" to the vast literature on spray combustion in engines. The scope of this chapter is as follows. After an introductory section, we will look at different phenomena in fuel sprays (e.g., with what speed and angle they move, how they break up, evaporate and ultimately combust). After that we discuss different classes of spray models, ranging from simple measurement-based correlations to full CFD models (without going into details on the latter). In the section 8 some (semi-)phenomenological models are treated in more detail, since these provide a good balance between simplicity and physical insight. Since the text was written for a post-graduate combustion course, the level of this chapter is slightly more advanced than the rest of the lecture notes. Therefore, from the models discussed, only the Sandia model belongs to the core part of the Fuels & Lubes course

Real gas effects in Siebers’ mixing-limited spray vaporization model

Lowering diesel engine emission levels, while preserving performance, is the main demand in the development of current and future diesel engines. To fulfill it, the in-cylinder vaporization and combustion processes of the diesel spray must be well understood. An important parameter in the vaporization process of a diesel spray is the maximal penetration distance of liquid fuel (i.e. the "liquid length"). So-called mixing-limited vaporization models assume that the vaporization rate of the fuel is limited by the mixing rate of fuel and ambient gas. Such models have been shown in the literature to accurately correlate liquid lengths for moderate to high in-cylinder densities, i.e. in the density range relevant to modern diesel engines. Since in-cylinder pressures can reach high absolute levels, real gas effects should be considered in these models. Critical evaluation of the most commonly used mixing-limited vaporization model (Siebers, SAE 1999-01-0528) reveals that real gas effects are not implemented consistently, since compressibility factors of the fuel and ambient gas are decoupled.In this work the Siebers model is adapted to properly include real gas effects, using saturated vapor fractions from equilibrium flash calculations based on the Peng-Robinson equation of state. Results of the original and revised models are compared to experimental liquid length data from Sandia National Laboratories for various fuels, densities and temperatures. At relatively low ambient densities, the original and revised models give identical results, as expected. At higher densities, more relevant to current and future diesel engines, the difference becomes significant. Moreover, liquid lengths computed with the revised model are closer to experimental data, especially at the highest ambient pressures. It is concluded that the overall predictive capability of the Siebers model can be improved using the method to include real gas effects presented here