Ccm Carlo Luijten

High pressure nucleation in water/nitrogen systems

Nucleation rate measurements of water in the presence of nitrogen as a carrier gas are reported at total pressures near 10, 25, and 40 bar, and temperatures of 230 and 250 K. The results were obtained using our pulse-expansion wave tube, particularly suited for high pressure nucleation research. Enhanced fugacity of water vapor in the mixture, due to the presence of nitrogen, was quantitatively taken into account. Values of the enhancement factors as a function of pressure and temperature were correlated from accurate gravimetric measurements available in literature. The results demonstrate a strong influence of nitrogen pressure on the nucleation behavior of water, when temperature and supersaturation are kept fixed. The effect is associated with a decrease of the surface tension of water, due to the adsorption of nitrogen onto the liquid surface. A tentative model is presented that qualitatively describes this decreasing surface tension with pressure. The competition between the opposing effects of enha...

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 ou...

Experimental Study of Fuel Composition Impact on PCCI Combustion in a Heavy-Duty Diesel Engine

Premixed Charge Compression Ignition (PCCI) is a combustion concept that holds the promise of combining emission levels of a spark-ignition engine with the efficiency of a compression-ignition engine. In a short term scenario, PCCI would be used in the lower load operating range only, combined with conventional diesel combustion at higher loads. This scenario relies on using near standard components and conventional fuels; therefore a set of fuels is selected that only reflects short term changes in diesel fuel composition. Experiments have been conducted in one dedicated test cylinder of a modified 6-cylinder 12.6 liter heavy duty DAF engine. This test cylinder is equipped with a stand-alone fuel injection system, EGR circuit and air compressor. For the low load operating range the compression ratio has been lowered to 12:1 by means of a thicker head gasket. It is shown that emission levels and performance strongly correlate with the combustion delay (CD=CA50-SOI), independent of how this combustion delay is achieved. In a longer term scenario, both engine hardware and fuels can be adapted to overcome intrinsic PCCI challenges. At higher loads and at 15:1 compression ratio, necessary for good full load efficiency, a less reactive fuel is required to delay auto-ignition and phase combustion correctly. A number of low reactivity fuel blends have been used to investigate the desired Cetane Number for PCCI operation at different loads. For these blends too, all emission levels as well as the efficiency are shown to greatly correlate with the combustion delay. With an improved efficiency because of the higher compression ratio, the blend with an estimated CN of 25 was found to be the most flexible in being able to choose the optimum CD for the conditions and load used.

Nucleation at high pressure. I. Theoretical considerations

A theoretical approach is presented that accounts for the influence of high pressure background gases on the vapor-to-liquid nucleation process. The key idea is to treat the carrier gas pressure as a perturbation parameter that modifies the properties of the nucleating substance. Two important mechanisms are identified in this respect: With increasing carrier gas pressure, the saturated vapor density tends to increase (enhancement effect), whereas the surface tension generally decreases. Several routes to obtain data for these pressure effects are outlined, in particular for the vapor–gas mixtures that have been studied experimentally. (The results of these expansion wave tube experiments are presented in Paper II of this paper [J. Chem. Phys. 111, 8535 (1999), following paper.]) Using classical nucleation theory, a criterion is then derived for the “pressure perturbation” approach to be valid: xgeq≪(S−1)/S, where xgeq is the carrier gas solubility in the liquid phase, and S is the supersaturation ratio. ...

Transitional droplet growth and diffusion coefficients

The droplet growth models of Gyarmathy and Young, valid for arbitrary Knudsen numbers, are compared with experimental growth results obtained from expansion wave tube experiments. Growth experiments of n-pentanol in helium were performed at approximately 1 bar, resulting in growth curves stretching from the transition regime OKn11U to the continuum regimeOKn 1). Droplet growth experiments of water in helium and water in nitrogen were performed at elevated pressures, when the mean free path is small; hence, these growth curves are situated near the continuum regime. For Kn > 0.1, the Gyarmathy model appears to describe the experimental growth curves better than the Young model. However, for Kn < 0.02, the Young model gives the best results. For the water‐ helium and water‐nitrogen systems new experimental diAusion coeAcients are obtained, which are in good

Gasoline–diesel dual fuel : effect of injection timing and fuel balance

Recently, some studies have shown high efficiencies using controlled auto-ignition by blending gasoline and diesel to a desired reactivity. This concept has been shown to give high efficiency and, because of the largely premixed charge, low emission levels. The origin of this high efficiency, however, has only partly been explained. Part of it was attributed to a lower temperature combustion, originating in lower heat losses. Another part of the gain was attributed to a faster, more Otto-like (i.e. constant volume) combustion. Since the concept was mainly demonstrated on one single test setup so far, an experimental study has been performed to reproduce these results and gain more insight into their origin. Therefore one cylinder of a heavy duty test engine has been equipped with an intake port gasoline injection system, primarily to investigate the effects of the balance between the two fuels, and the timing of the diesel injection. Besides studying trends in the dual-fuel regime, this also allows to find best points to compare with conventional diesel combustion. Results show that compared to more conventional combustion regimes, this dual-fuel concept can escape from the common NOx-smoke trade-off, reducing both to near-zero values. Although hydrocarbon emissions are somewhat increased, indicated efficiencies are significantly improved. The absolute efficiencies are not as high as reported in other work, but the increase does confirm the potential of the concept. The increase in indicated efficiency is shown to originate from a higher thermal efficiency, because short burn durations at high gasoline fractions enable for CA50 to be phased closer to TDC, without combustion occurring too much before TDC. Pressure rise rates are as low as with conventional diesel combustion, when using the same Exhaust Gas Recirculation (EGR) percentage. Although the dual fuel concept has a much higher rate of heat release, this is phased better after TDC. A dedicated set of experiments has also shown that the late-cycle diesel injection is dominant in combustion phasing and that control has to be found in this diesel injections.

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 results.

Survivability of thermographic phosphors (YAG:Dy) in a combustion environment

The feasibility of applying laser-induced phosphorescence in a combustion environment was shown by testing the consistency of the emission‐temperature relations of thermographic phosphor particles (YAG:Dy). The relations were calibrated before and after the phosphor particles had passed a flame front. The calibrations were performed in air and in pure oxygen. The emission‐temperature relation prevails from around 300 K to 1300 K. The difference in emission‐temperature relation for the two different cases is less than the experimental precision (3%).

Binary nucleation rate measurements of n‐nonane/methane at high pressures

We present homogeneous nucleation rates in the binary mixture n‐nonane/methane in the supercritical regime, measured in a new pulse expansion tube at pressures up to 40 bar, at a temperature of 240 K. It is shown that both n‐nonane and methane are present in the critical cluster. The critical supersaturation of n‐nonane decreases from 30 at 10 bar, down to 6 at 40 bar total pressure.

Throttle loss recovery using a variable geometry turbine

Two of the most pressing challenges of the automotive sector are reduction of fuel consumption and corresponding emission of greenhouse gases, especially when taking into account the growing degree of luxury in modern passenger cars, which increases the auxiliary load on the engine. Preferably, this increase in auxiliary load is compensated by the recovery of waste energy. To accomplish this, a technology called WEDACS (Waste Energy Driven Air Conditioning System) is being developed to recover throttling losses. WEDACS uses a turbine to induce provide the engine with the same air mass flow rate as a throttle valve while producing mechanical energy and cold air. An alternator coupled to this turbine converts mechanical energy into electrical energy and the cold air is used to cool A/C fluid. This way the load of both the engine-mounted alternator and A/C compressor is reduced or eliminated, resulting in higher efficiency. A previous paper provides a proof of principle, using a turbine from a turbocharger, but also discusses a challenge in the form of a limited operating range. The present paper focuses on addressing this challenge. To expand the control range of the engine, a turbocharger with variable nozzle turbine is used. Due to limitations in the variable nozzle mechanism, the range is limited to higher engine powers. It is shown that between 50 W and 1.3 kW of energy can be recovered from a 2-liter engine, depending on the operating point. A second turbochargers variable nozzle mechanism is adapted to enable control of a 2-liter engine from idle to about 50% engine power. With decreasing engine power, the energy recovery efficiency eventually drops to zero. The root cause for this is identified and an attempt is made to improve efficiency. Finally the drive cycle model from the previous paper is expanded and a new drive cycle simulation shows a fuel consumption improvement over the NEDC of about 5 to 8% for a mid-sized passenger car with a 2-liter engine.