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A detailed description of a numerical method for computing unsteady flows in engine intake and exhaust systems is given. The calculations include the effects of heat transfer and friction. The inclusion of such calculations in a mathematically simulated engine cycle is discussed and results shown for several systems. In particular, the effects of bell-mouth versus plain pipe terminations and the effects of a finite surge tank are calculated. Experimental data on the effect of heat transfer from the back of the intake valve on wave damping are given and show the effect to be negligible. Experimental data on wave damping during the valve closed period and on the temperature rise of the air near the valve are also given.

The ratio of two temperature gradients across the combustion-chamber wall in a diesel engine is used to provide a heat flow ratio showing the radiant heat transfer as a per cent of local total heat transfer. The temperature gradients were obtained with a thermocouple junction on each side of the combustion-chamber wall. The first temperature gradient was obtained by covering the thermocouple at the cylinder gas-wall interface with a thin sapphire window, while the second was obtained without the window. Results show that the time-average radiant heat transfer is of significant magnitude in a diesel engine, and is probably even more significant in heat transfer during combustion and expansion.

Particle image velocimetry measurements of the in-cylinder flow in an optically accessible single-cylinder research engine were taken to better understand the effects of intake pressure variations on the flow field. At a speed of 1500 rpm, the engine was run at six different intake pressure loads from 0.4 to 0.95 bar under motored operation. The average velocity fields show that the tumble center position is located closer to the piston and velocity magnitudes decrease with increasing pressure load. A closer investigation of the intake flow near the valves reveals sharp temporal gradients and differences in maximum and minimum velocity with varying intake pressure load which are attributed to intake pressure oscillations. Despite measures to eliminate acoustic oscillations in the intake system, high-frequency pressure oscillations are shown to be caused by the backflow of air from the exhaust to the intake pipe when the valves open, exciting acoustic modes in the fluid volume.

The objective of this research was to investigate the effect of injection pressure on air entrainment into transient diesel sprays. The main application of interest was the direct injection diesel engine. Particle Image Velocimetry was used to make measurements of the air entrainment velocities into a spray plume as a function of time and space. A hydraulically actuated, electronically controlled unit injector (HEUI) system was used to supply the fuel into a pressurized spray chamber. The gas chamber density was maintained at 27 kg/m3. The injection pressures that were studied in this current research project were 117.6 MPa and 132.3 MPa. For different injection pressures, during the initial two-thirds of the spray plume there was little difference in the velocities normal to the spray surface. For the last third of the spray plume, the normal velocities were 125% higher for the high injection pressure case.

Cycle-to-cycle variations in internal combustion engines are known to lead to limitations in engine load and efficiency, as well as increases in emissions. Recent research has led to the identification of the source of cyclic variations of pressure, soot and NO emissions in direct injection common rail diesel engines, when employing a single block injection and operating under long ignition delay conditions. The variations in peak pressure arise from changes in the diffusion combustion rate, caused by randomly occurring in-cylinder pressure fluctuations. These fluctuations result from the excitation of the first radial mode of vibration of the cylinder gases which arises from the rapid premixed combustion after the long ignition delay period. Cycles with high-intensity fluctuations present faster diffusion combustion, resulting in higher cycle peak pressure, as well as higher measured exhaust NO concentrations.

Past research has shown that post injections have the potential to reduce Diesel engine exhaust PM concentration without any significant influence in NOx emissions. However, an accurate, widely applicable rule of how to parameterize a post injection such that it provides a maximum reduction of PM emissions does not exist. Moreover, the underlying mechanisms are not thoroughly understood. In past research, the underlying mechanisms have been investigated in engine experiments, in constant volume chambers and also using detailed 3D CFD-CMC simulations. It has been observed that soot reduction due to a post injection is mainly due to two reasons: increased turbulence from the post injection during soot oxidation and lower soot formation due to lower amount of fuel in the main combustion at similar load conditions. Those studies do not show a significant temperature rise caused by the post injection.

Measurements of the soot emissions and engine operating parameters from a diesel engine during transient operation were used to investigate the influence of transient operation on the soot emissions, as well as to validate a realtime mean value soot model (MVSM, [1]) for transient operation. To maximize the temporal resolution of the soot emission and engine parameter measurements (in particular EGR), fast instruments were used and their dynamic responses characterized and corrected. During tip-in transients, an increase in the soot emissions was observed due to a short term oxygen deficit compared to steady-state operation. No significant difference was seen between steady-state and transient operation for acceleration transients. When the MVSM was provided with inputs of sufficient temporal resolution, it was capable of reproducing the qualitative and, in part, quantitative soot emission trends.

A detailed mathematical model of the thermodynamic events of a crankcase scavenged, two-stroke, SI engine is described. The engine is divided into three thermodynamic systems: the cylinder gases, the crankcase gases, and the inlet system gases. Energy balances, mass continuity equations, the ideal gas law, and thermodynamic property relationships are combined to give a set of coupled ordinary differential equations which describe the thermodynamic states encountered by the systems of the engine during one cycle of operation. A computer program is used to integrate the equations, starting with estimated initial thermodynamic conditions and estimated metal surface temperatures. The program iterates the cycle, adjusting the initial estimates, until the final conditions agree with the beginning conditions, that is, until a cycle results.

Optical soot pyrometry is a mature experimental technique that has been applied to a broad range of combustion systems for measuring soot temperature and concentration. Even though the method is widely used and well documented, the line of sight nature of the technique makes the interpretation of its results challenging. Notably, gradients in temperature and soot concentration along the line of sight or across the field of view can introduce significant levels of uncertainty in the results. This paper presents a numerical study where the signal from the experimental two-color pyrometry technique in a marine diesel engine reference experiment is reconstructed employing computational fluid dynamics (CFD) and a detailed Line-by-Line (LBL) spectral radiation model. The analysis is aimed at qualitatively supporting interpretability of experimental observations.

Highly time resolved measurements of cylinder pressure acquired simultaneously from three transducers were used to investigate the nature of knocking combustion and to identify biases that the pressure measurements induce. It was shown by investigating the magnitude squared coherence (MSC) between the transducer signals that frequency content above approximately 40 kHz does not originate from a common source, i.e., it originates from noise sources. The major source of noise at higher frequency is the natural frequency of the transducer that is excited by the impulsive knock event; even if the natural frequency is above the sampling frequency it can affect the measurements by aliasing. The MSC analysis suggests that 40 kHz is the appropriate cutoff frequency for low-pass filtering the pressure signal. Knowing this, one can isolate the knock event from noise more accurately.

A computational, three-dimensional approach to investigate the behavior of diesel soot particles in the micro-channels of wall-flow Diesel Particulate Filters is presented. The KIVA3V CFD code, already extended to solve the 2D conservation equations for porous media materials [1], has been enhanced to solve in 2-D and 3-D the governing equations for reacting and compressible flows through porous media in non axes-symmetric geometries. With respect to previous work [1], a different mathematical approach has been followed in the implementation of the numerical solver for porous media, in order to achieve a faster convergency as source terms were added to the governing equations. The Darcy pressure drop has been included in the Navier-Stokes equations and the energy equation has been extended to account for the thermal exchange between the gas flow and the porous wall.

3-D Computational Fluid Dynamics (CFD) simulations have been performed to study particulate formation in a Spark-Ignition (SI) engine under premixed conditions. A semi-detailed soot model and a chemical kinetic model, including poly-aromatic hydrocarbon (PAH) formation, were coupled with a spark ignition model and the G equation flame propagation model for SI engine simulations and for predictions of soot mass and particulate number density. The simulation results for in-cylinder pressure and particle size distribution (PSDs) are compared to available experimental studies of equivalence ratio effects during premixed operation. Good predictions are observed with regard to cylinder pressure, combustion phasing and engine load. Qualitative agreements of in-cylinder particle distributions were also obtained and the results are helpful to understand particulate formation processes.

This study investigates n-dodecane split injections of “Spray A” from the Engine Combustion Network (ECN) using two different turbulence treatments (RANS and LES) in conjunction with a Conditional Moment Closure combustion model (CMC). The two modeling approaches are first assessed in terms of vapor spray penetration evolutions of non-reacting split injections showing a clearly superior performance of the LES compared to RANS: while the former successfully reproduces the experimental results for both first and second injection events, the slipstream effect in the wake of the first injection jet is not accurately captured by RANS leading to an over-predicted spray tip penetration of the second pulse. In a second step, two reactive operating conditions with the same ambient density were investigated, namely one at a diesel-like condition (900K, 60bar) and one at a lower temperature (750K, 50bar).

The performance of a structural design significantly depends upon the assumptions made on input load. In order to estimate the input load, during the design and development stage of the suspension assembly of a BAJA car, designers and analysts invest immense amount of time and effort to formulate the mathematical model of the design. These theoretical formulations may include idealization errors which can affect the performance of the car as a final product. Due to the errors associated with the assumption of design load, several components might have more weight or may have less strength than needed. This discrepancy between the assumed input load (lab or theoretical studies) and the actual load from the environment can be eliminated by performing a real life testing process using load recovery methodology. Commercial load cells exist in industry to give engineers insight to understanding the complex real world loading of their structures.

Sector mesh modeling is the dominant computational approach for combustion system design optimization. The aim of this work is to quantify the errors descending from the sector mesh approach through three geometric modeling approaches to an optical diesel engine. A full engine geometry mesh is created, including valves and intake and exhaust ports and runners, and a full-cycle flow simulation is performed until fired TDC. Next, an axisymmetric sector cylinder mesh is initialized with homogeneous bulk in-cylinder initial conditions initialized from the full-cycle simulation. Finally, a 360-degree azimuthal mesh of the cylinder is initialized with flow and thermodynamics fields at IVC mapped from the full engine geometry using a conservative interpolation approach. A study of the in-cylinder flow features until TDC showed that the geometric features on the cylinder head (valve tilt and protrusion into the combustion chamber, valve recesses) have a large impact on flow complexity.

The higher cylinder peak pressure and pressure rise rate of modern diesel and gasoline fueled engines tend to increase combustion noise while customers demand lower noise. The multiple degrees of freedom in engine control and calibration mean there is more scope to influence combustion noise but this must first be measured before it can be balanced with other attributes. An efficient means to realize this is to calculate combustion noise from the in-cylinder pressure measurements that are routinely acquired as part of the engine development process. This publication reviews the techniques required to ensure accurate and precise combustion noise measurements. First, the dynamic range must be maximized by using an analogue to digital converter with sufficient number of bits and selecting an appropriate range in the test equipment.

The University of Wisconsin-Madison Snowmobile Team has designed and constructed a clean, quiet, high performance snowmobile for entry in the 2008 Society of Automotive Engineers' Clean Snowmobile Challenge. Built on a 2003 cross-country touring chassis, this machine features a 750 cc fuel-injected four-stroke engine equipped with a fuel sensor which allows operation ranging from regular gasoline to an 85% blend of ethanol and gasoline (E85). The engine has been customized with a Mototron control system which allows for full engine optimization using a range of fuels from E00 to E85. Utilizing a heated oxygen sensor and a 3-way catalyst customized for this engine by W.C. Heraeus-GmbH, this sled reduces NOx, HC and CO emissions by up to 89% to an average specific mass of 0.484, 0.154, 4.94 g/kW-hr respectively. Finally, the Mototron system also allowed Wisconsin to extract another 4 kW from the Weber 750cc engine; producing 45 kW and 65 Nm of torque.

In recent years society's demand and interest in clean and efficient internal combustion engines has grown significantly. Several ideas have been proposed and tested to meet this demand. In particular, dual-fuel Reactivity Controlled Compression Ignition (RCCI) combustion has demonstrated high thermal efficiency, and low engine-out NOx, and soot emissions. Unlike homogeneous charge compression ignition (HCCI) combustion, which solely relies on the chemical kinetics of the fuel for ignition control, RCCI combustion has proven to provide superior combustion controllability while retaining the known benefits of low emissions and high thermal efficiency of HCCI combustion. However, in order for RCCI combustion to be adopted as a high efficiency and low engine-out emission solution, it is important to achieve high-power operation that is comparable to conventional diesel combustion (CDC).

The CFD tools in aerodynamic design process have been commonly used in aerospace industry in last three decades. Although there are many CFD software algorithms developed for aerodynamic applications, the nature of a complex, three-dimensional geometry in incompressible highly separated, viscous flow made computational simulation of ground vehicle aerodynamics more difficult than aerospace applications. However, recent developments in computational hardware and software industry enabled many new engineering applications on computational environment. Traditional production process has largely influenced by computational design, analysis, manufacturing and visualization. Different aspects of linking advanced computational tools and aerodynamic vehicle design challenges are discussed in the present work. Key technologies like parallel computation, turbulence modeling and CFD/wind tunnel compatibility issues are presented.

The interaction of turbulent premixed methane combustion with the surrounding flow field can be studied using optically accessible test rigs such as a rapid compression expansion machine (RCEM). The high flexibility offered by such a test rig allows its operation at various thermochemical conditions at ignition. However, limitations inherent to such test rigs due to the absence of an intake stroke do not allow turbulence production as found in IC-engines. Hence, means to introduce turbulence need to be implemented and the relevant turbulence quantities have to be identified in order to enable comparability with engine relevant conditions. A dedicated high-pressure direct injection of air at the beginning of the compression phase is considered as a measure to generate adjustable turbulence intensities at spark timing and during the early flame propagation.