Search Results

Turbulent jet ignition is a pre-chamber ignition enhancement method that produces a distributed ignition source through the use of a chemically active turbulent jet which can replace the spark plug in a conventional spark ignition engine. In this paper combustion visualization and characterization was performed for the combustion of a premixed propane/air mixture initiated by a pre-chamber turbulent jet ignition system with no auxiliary fuel injection, in a rapid compression machine. Three different single orifice nozzles with orifice diameters of 1.5 mm, 2 mm, and 3 mm were tested for the turbulent jet igniter pre-chamber over a range of air to fuel ratios. The performance of the turbulent jet ignition system based on nozzle orifice diameter was characterized by considering both the 0-10 % and the 10-90 % burn durations of the pressure rise due to combustion.

Autoignition delay times of two full blend gasoline fuels (high and low RON) were explored in a rapid compression machine. CO2 dilution by mass was introduced at 0%, 15%, and 30% levels with the O2:N2 mole ratio fixed at 1:3.76. This dilution strategy is used to represent exhaust gas recirculation (EGR) substitution in spark ignition (SI) engines by using CO2 as a surrogate for major EGR constituents(N2, CO2, H2O). Experiments were conducted over the temperature range of 650K-900K and at 10 bar and 20 bar compressed pressure conditions for equivalence ratios of (Φ =) 0.6-1.3. The full blend fuels were admitted directly into the combustion chamber for mixture preparation using the direct test chamber (DTC) approach. CO2 addition retarded the autoignition times for the fuels studied here. The retarding effect of the CO2 dilution was more pronounced in the NTC region when compared to the lower and higher temperature range.

Continuous efforts to improve thermal efficiency and reduce exhaust emissions of internal combustion engines have resulted in development of various solutions towards improved lean burn ignition systems in spark ignition engines. The Dual Mode, Turbulent Jet Ignition (DM-TJI) system is one of the leading technologies in that regard which offers higher thermal efficiency and reduced NOx emissions due to its ability to operate with very lean or highly dilute mixtures. Compared to other pre-chamber ignition technologies, the DM-TJI system has the distinct capability to work with a very high level of EGR dilution (up to ~40%). Thus, this system enables the use of a three-way catalyst (TWC). Auxiliary air supply for pre-chamber purge allows this system to work with such high EGR dilution rate. This work presents the results of experimental investigation carried out with a Dual Mode, Turbulent Jet Ignition (DM-TJI) optical engine equipped with a cooled EGR system.

Over the years, many studies have examined the natural gas flame characteristics with either CO2, H2O, or N2 dilution in order to investigate the exhaust gas recirculation (EGR) effect on the performance of natural gas vehicles. However, studies analyzing the actual EGR concentration are very scarce. In the present study, spherically expanding flames were employed to investigate the EGR effect on the laminar flame speed (LFS) and the burned gas Markstein length (Lb) of premixed CH4/air flames at 373 K and 3 bar. The EGR mixture was imitated with a mixture of 9.50% CO2 + 19.01% H2O + 71.49% N2 by mole. EGR ratios of 0%, 5%, 10%, and 15% were tested. Experimental results show that LFS values are lowered by 20-23%, 38-43% and 53-54% due to 5%, 10% and 15% EGR, respectively. Additionally, it was observed that Lb values slightly increase at high equivalence and EGR ratios, where CH4 flames are more stable and more stretched.

The identification/localization of propulsion noise in turbo machinery plays an important role in its design and in noise mitigation techniques. Near field acoustic holography (NAH) is the process by which all aspects of the sound field can be reconstructed based on sound pressure measurements in the near field domain. Identification of noise sources, particularly in turbo-machinery applications, efficiently and accurately is difficult due to complex noise generation mechanisms. Backward prediction of the sound field closer to the source than the measurement plane is typically an unstable “ill-posed” inverse problem due to the presence of measurement noise. Therefore regularized inversion techniques are typically implemented for noise source reconstruction. Another major source of ill-posedness in NAH inverse problems is a larger number of unknowns (sources) than available pressure measurements. A model reduction technique is proposed in this paper to address this issue.

In order to improve the reliability of fan design and the prediction of underhood engine cooling based on CFD, Valeo Motors and Actuators and Michigan State University have teamed up to develop a comprehensive experimental and numerical database. The initial focus has been on the simulations of the isolated fan environment in two different test facilities. To understand the discrepancies observed in the comparisons of integral performances, the first detailed hot wire measurements on the MSU test facility have been collected. The data are split into mean velocity components and RMS fluctuations. The former are successfully compared to three detailed turbulent numerical simulations of the corresponding facilities.

A numerical study on the combustion of Methanol in a directly injected (DI) engine was conducted. The study considers the effect of the bowl-in-piston (BIP) geometry, swirl ratio (SR), and relative equivalence ratio (λ), on flame propagation and burn rate of Methanol in a 4-stroke engine. Ignition-assist in this engine was accomplished by a spark plug system. Numerical simulations of two different BIP geometries were considered. Combustion characteristics of Methanol under swirl and no-swirl conditions were investigated. In addition, the amount of injected fuel was varied in order to determine the effect of stoichiometry on combustion. Only the compression and expansion strokes were simulated. The results show that fuel-air mixing, combustion, and flame propagation was significantly enhanced when swirl was turned on. This resulted in a higher peak pressure in the cylinder, and more heat loss through the cylinder walls.

Three dimensional numerical simulation of the transient turbulent jet and ignition processes of a premixed methane-air mixture of a turbulent jet ignition (TJI) system is performed using Converge computational software. The prechamber initiated combustion enhancement technique that is utilized in a TJI system enables low temperature combustion by increasing the flame propagation rate and therefore decreasing the burn duration. Two important components of the TJI system are the prechamber where the spark plug and injectors are located and the nozzle which connects the prechamber to the main chamber. In order to model the turbulent jet of the TJI system, RANS k-ε and LES turbulent models and the SAGE chemistry solver with a reduced mechanism for methane are used.

EGR coolers are used in combustion engines to reduce NOx emissions. However, heat transfer in these coolers also results in thermophoresis-temperature-gradient driven motion of suspended particles towards cooler regions-which leads to significant soot deposition. A simple one-dimensional model is proposed to predict the deposition velocity and soot layer thickness that compares reasonably well with experimental data. The behavior of soot deposits on cooled surfaces is complex, with the thickness of the soot layer stabilizes after around 100 hours, reaching a uniform, thickness over the entire heat-exchanger surface. An analysis of this trend and a tentative mechanism to explain this type of behavior is given, based on experimental observations.

High frequency variations in crankcase pressure have been observed in Inline-four cylinder (I4) engines and an understanding of the causes, frequency and magnitude of these variations is helpful in the design and effective operation of various engine systems. This paper shows through a review and explanation of the physics related to engine operation followed by comparison to measured vehicle data, the relationship between crankcase volume throughout the engine cycle and the observed pressure fluctuations. It is demonstrated that for a known or proposed engine design, through knowledge of the key engine design parameters, the frequency and amplitude of the cyclic variation in crankcase pressure can be predicted and thus utilized in the design of other engine systems.

In-cylinder visualization experiments were completed using an International VT275-based optical DI Diesel engine operating under high simulated exhaust gas recirculation combustion conditions. Experiments were run at four load conditions to examine variations in fuel spray, combustion, and soot production. Mass fraction burned analyses of pressure data were used to investigate the combustion processes of the various operating conditions. An infrared camera was used to visualize fuel spray events and exothermic combustion gases. A visible, high-speed camera was used to image natural luminosity produced by soot. The recorded images were post-processed to analyze the fuel spray, the projected exothermic areas produced by combustion, as well as soot production of different load conditions. Probability maps of combustion and fuel spray occurrence in the cylinder are presented for insight into the combustion processes of the different conditions.

A direct-injection and spark-ignition single-cylinder engine with optical access to the cylinder was used for the combustion visualization study. Gasoline and ethanol-gasoline blended fuels were used in this investigation. Experiments were conducted to investigate the effects of fuel injection pressure, injection timing and the number of injections on the in-cylinder combustion process. Two types of direct fuel injectors were used; (i) high-pressure production injector with fuel pressures of 5 and 10 MPa, and (ii) low-pressure production-intent injector with fuel pressure of 3 MPa. Experiments were performed at 1500 rpm engine speed with partial load. In-cylinder pressure signals were recorded for the combustion analyses and synchronized with the high-speed combustion imaging recording. Visualization results show that the flame growth is faster with the increment of fuel injection pressure.

A multicomponent droplet evaporation model which discretizes the one-dimensional mass and temperature profiles inside a droplet with a finite volume method has been developed and implemented into a large-eddy simulation (LES) model for spray simulations. The LES and multicomponent models were used along with the KH-RT secondary droplet breakup model to simulate realistic fuel sprays in a closed vessel. The effect of various spray and ambient gas parameters on the liquid penetration length of different single component and multicomponent fuels was investigated. The numerical results indicate that the spray penetration length decreases non-linearly with increasing gas temperature or pressure and is less sensitive to changes in ambient gas conditions at higher temperatures or pressures. The spray models and LES were found to predict the experimental results for n-hexadecane and two multicomponent surrogate diesel fuels reasonably well.

An experimental study has been conducted to quantify the velocity and pressure inside an idealized intake manifold of a motored internal combustion engine assembly. The aim of this work is to provide the real-time boundary conditions for more accurate multi-dimensional numerical simulations of complex in-cylinder flows in an internal combustion engine as well as the resultant in-cylinder flow patterns. The geometry of the intake manifold is simplified for this purpose. A hot-wire anemometer and a piezoresistive absolute pressure transducer are used to measure the velocity and pressure, respectively, over a plane inside the circular section of the intake manifold. In addition, pressure measurements are performed over an elliptical section near the intake port. Phase-averaged velocity and pressure profiles are then calculated from the instantaneous measurements. Experiments were performed at 900 and 1200 rpm engine speeds with wide open throttle.

Cavitation induced cylinder liner erosion can be a significant durability problem in high power density diesel engines. It is typically discovered in the field, thus causing costly redesigns. The application of a predictive simulation to analyze the liner cavitation process upfront could identify the problem early on and enable significant savings. Hence, this work investigates the ability of the computational fluid dynamics (CFD) multiphase flow simulation tool to handle vibration induced cavitation. A flow of liquid through a U-shaped duct is analyzed, where a middle segment of the duct is set to vibrate in a manner resembling vibration of the cooling jacket walls in an internal combustion engine. Velocity, pressure and vapor concentration fields are tracked for two cases, distinguished by different frequencies of duct wall vibration.

Aromatics have long been used in pump-grade gasoline to inhibit engine knock and enhance a fuel’s octane number, therefore this study focuses on how the addition of aromatics at 2% by mole affects the ignition characteristics of a Toluene Reference Fuel (TRF). The additives investigated in this study are the substituted phenols p-cresol and 2,6-xylenol. In addition to fuel composition, exhaust gas recirculation dilution can be used to lower the combustion temperature and consequently lengthen the ignition delay time of a given fuel-air mixture. This study replicated exhaust gas recirculation dilution by using N2, as it was inert and did not interfere with reactions between the fuel and oxidizer. Determination of whether the similar structures of p-cresol and 2,6-xylenol result in different autoignition inhibiting characteristics was performed on a rapid compression machine.

Ignition delay, using a rapid compression machine (RCM), is defined as the time period between the end of compression and the maximum rate of pressure rise due to combustion, at a given compressed condition of temperature and pressure. The same compressed conditions can be reached by a variety of combinations of compression ratio, initial temperature, initial pressure, diluent gas composition, etc. It has been assumed that the value of ignition delay, for a given fuel and at a given set of compressed conditions, would be the same, irrespective of the variety of the above-mentioned combinations that were used to achieve the compressed conditions. In this study, a range of initial conditions and compression ratios are studied to determine their effect on ignition delay time and to show how ignition delay time can differ even at the same compressed conditions.

Iso-Octane (2,2,4-trimethlypentane) is an important gasoline primary reference fuel (PRF) surrogate. Auto ignition of iso-octane was examined using a rapid compression machine (RCM) with iso-octane, air and carbon dioxide (CO2) mixtures. Experiments were conducted over a temperature range of 650K-900K at 20bar and 10 bar compressed conditions for equivalence ratios (Φ =) 0.6, 0.8, 1.0 and 1.3. CO2 dilution by mass was introduced at 0%, 15% and 30% levels with the O2:N2 mole ratio fixed at 1:3.76 emulating the exhaust gas recirculation (EGR) substitution in spark ignition (SI) engines. In this study the direct test chamber (DTC) approach is used for introducing iso-octane directly into the RCM test chamber via a direct injector. The results using this approach are compared with other RCM data available in the literature at undiluted Φ = 1.0 and 20 bar compressed pressure and show good agreement.

Mixture formation and combustion dynamics are the primary contributors to the performance and emission characteristics of direct-injected spark ignition (SI) engines. This requires assessing the benefits and tradeoffs of the design and control factors that influence mixing and the subsequent combustion event. In this study, Taguchi's L18 orthogonal array design of experiment (DoE) methodology has been applied to assess contributions and tradeoffs of varied compression ratio, piston bowl design, intake port tumble design, injector spray pattern, injection timing, injection pressure, exhaust gas recirculation (EGR) rate, and intake valve closing timing in a single-cylinder boosted gasoline direct injection (GDI) SI engine. This multiparameter study has been carried out across three speed-load conditions representative of typical automotive application operating ranges.

Fully three-dimensional computational fluid dynamic simulations with detailed chemistry of a single-orifice turbulent jet ignition device installed in a rapid compression machine are presented. The simulations were performed using the computational fluid dynamics software CONVERGE and its RANS turbulence models. Simulations of propane fueled combustion are compared to data collected in the optically accessible rapid compression machine that the model's geometry is based on to establish the validity and limitations of the simulations and to compare the behavior of the different air-fuel ratios that are used in the simulations.