Harold Schock

A Review of Pre-Chamber Initiated Jet Ignition Combustion Systems

This paper reviews progress on turbulent jet ignition systems for otherwise standard spark ignition engines, with focus on small pre-chamber systems (<3% of clearance volume) with auxiliary prechamber fueling. The review covers a range of systems including early designs such as those by Gussak and Oppenheim and more recent designs proposed by GM, FEV, Bosch and MAHLE Powertrain. A major advantage of jet ignition systems is that they enable very fast burn rates due to the ignition system producing multiple, distributed ignition sites, which consume the main charge rapidly and with minimal combustion variability. The locally distributed ignition sites allow for increased levels of dilution (lean burn/EGR) when compared to conventional spark ignition combustion. Dilution levels are comparable to those reported in recent homogeneous charge compression ignition (HCCI) systems. In addition, jet ignition systems have the potential for combustion phasing control and hence speed/load range benefits when compared to HCCI, without the need for SI-HCCI combustion mode switching. The faster burn rates also allow for a base compression ratio increase (1-2 points) when compared to spark ignition and when combined with diluted mixture combustion, provide increased engine efficiency.

Spark Ignition and Pre-Chamber Turbulent Jet Ignition Combustion Visualization

Natural gas is a promising alternative fuel as it is affordable, available worldwide, has high knock resistance and low carbon content. This study focuses on the combustion visualization of spark ignition combustion in an optical single cylinder engine using natural gas at several air to fuel ratios and speed‐load operating points. In addition, Turbulent Jet Ignition optical images are compared to the baseline spark ignition images at the world‐wide mapping point (1500 rev/min, 3.3 bar IMEPn) in order to provide insight into the relatively unknown phenomenon of Turbulent Jet Ignition combustion. Turbulent Jet Ignition is an advanced spark initiated pre‐chamber combustion system for otherwise standard spark ignition engines found in current passenger vehicles. This next generation pre‐chamber design simply replaces the spark plug in a conventional spark ignition engine. Turbulent Jet Ignition enables very fast burn rates due to the ignition system producing multiple, widely distributed ignition sites, which consume the main charge rapidly. This high energy ignition results from the partially combusted (reacting) pre‐chamber products initiating combustion in the main chamber. The distributed ignition sites enable relatively small flame travel distances enabling short combustion durations and high burn rates. Multiple benefits include extending the knock limit and initiating combustion in very dilute mixtures (excess air and/or EGR), with dilution levels being comparable to other low temperature combustion technologies (HCCI), without the complex control drawbacks.

Characterization of dry milled powders of LAST (lead–antimony–silver–tellurium) thermoelectric material

Although thermoelectric (TE) materials are often fabricated as cast ingots, there has been recent interest in the powder processing of these materials. Cast TE materials typically have grain sizes as large as several hundred microns, but powder processing (grinding, milling and then sintering) can produce dense specimens with a reduced grain size, an improved mechanical integrity and enhanced TE properties. In the TE literature when powder processing is employed, little or no description is provided of the powder processing techniques and the powder processing parameters are either not characterized or only a mean particle size is given. In this study, powders milled from solid cast ingots of the TE compound LAST (lead–antimony–silver–tellurium) were characterized via Coulter Counter, to measure the mean powder particle size and the size distribution, scanning electron microscopy (SEM), to examine the powder particle morphology, and X-ray diffraction (XRD), to detect possible phase changes or amorphization. The impurity levels in the milled powders were examined by wear rate measurements on the milling media, as well as by energy dispersive X-ray analysis and inductively coupled plasma measurements.

Young's modulus as a function of composition for an n-type lead-antimony-silver-telluride (LAST) thermoelectric material

For 17 cast lead–antimony–silver–telluride (LAST) thermoelectric specimens (representing 14 different chemical compositions), a combination of Vickers and Knoop microindentation techniques were used to determine the composition-dependent Youngs modulus, E, which ranged from 24 to 68 GPa. Following microindentation, independent nanoindentation measurements were also performed on 10 of the 17 specimens. In the literature, for pseudobinary joins in ternary or quaternary compounds (with the compositions A x B1– x C or A x B1– x CD, respectively), changes in the Youngs modulus have been expressed as quadratic functions of the compositional parameter x. In this study, we extend the quadratic functional form to a paraboloid in four composition variables to describe composition-dependent changes in E for the LAST compounds. Also, the composition-dependent changes in LAST are compared to the trends observed in the literature for E and bulk modulus for systems described by a single compositional variable.

Weibull analysis of the biaxial fracture strength of a cast p-type LAST-T thermoelectric material

This is the first study applying Weibull statistics to the strength distribution of a thermoelectric (TE) material and to determine the fracture strength of a member of the LAST-T (lead–antimony–silver–tellurium–tin) family of high-temperature TE compounds. The p-type TE material Ag0.9Pb9Sn9Sb0.6Te20 was cast from the melt and specimens cut from the resulting ingot were fractured in a ball-on-ring biaxial fracture test. The Weibull parameters (characteristic strength and Weibull modulus) were obtained from the fracture data. Implications of the Weibull analysis on the fabrication of TE devices are discussed.

A Study of Cycle-to-Cycle Variations and the Influence of Charge Motion Control on In-Cylinder Flow in an IC Engine

An experimental study is performed to investigate the cycle-to-cycle variations and the influence of charge motion control on in-cylinder flow measurement inside an internal combustion engine assembly. Molecular tagging velocimetry (MTV) is used to obtain the multiple point measurement of the instantaneous velocity field. MTV is a molecular counterpart of particle-based techniques, and it eliminates the use of seed particles. A two-component velocity field is obtained at various crank angle degrees for tumble and swirl measurement planes inside an optical engine assembly (1500 rpm and 2500 rpm engine speeds). Effects of charge motion control are studied considering different cases of: (i) charge motion control valve (CMCV) deactivated and (ii) CMCV activated. Both the measurement planes are used in each case to study the cycle-to-cycle variability inside an engine cylinder. Probability density functions of the normalized circulation are calculated from the instantaneous planar velocity to quantify the cycle-to-cycle variations of in-cylinder flows. In addition, the turbulent kinetic energy of flow is calculated and compared with the results of the probability density function. Different geometries of CMCV produce different effects on the in-cylinder flow field. It is found that the charge motion control used in this study has a profound effect on cycle-to-cycle variations during the intake and early compression; however, its influence reduces during the late compression. Therefore, it can be assumed that CMCV enhances the fuel-air mixing more than the flame speed.

A High Speed Flow Visualization Study of Fuel Spray Pattern Effect on Mixture Formation in a Low Pressure Direct Injection Gasoline Engine

In developing a direct injection gasoline engine, the incylinder fuel air mixing is key to good performance and emissions. High speed visualization in an optically accessible single cylinder engine for direct injection gasoline engine applications is an effective tool to reveal the fuel spray pattern effect on mixture formation The fuel injectors in this study employ the unique multi-hole turbulence nozzles in a PFI-like (Port Fuel Injection) fuel system architecture specifically developed as a Low Pressure Direct Injection (LPDI) fuel injection system. In this study, three injector sprays with a narrow 40° spray angle, a 60°spray angle with 5°offset angle, and a wide 80° spray angle with 10° offset angle were evaluated. Image processing algorithms were developed to analyze the nature of in-cylinder fuel-air mixing and the extent of fuel spray impingement on the cylinder wall. Test data reveal that for a given cylinder head, piston configuration and intake air port flow characteristics, injector spray pattern plays a dominating role in how the fuel-air mixture is formed. If an appropriate injector spray pattern is chosen, the in-cylinder fuel mixing can be enhanced by minimizing fuel impingement on cylinder wall, piston top, and intake valves, thus producing a more homogeneous fuel-air mixture prior to the ignition. Engine designers can select a specific spray pattern to improve the fuel-air mixture optimized for specific parameters such as engine head, piston, valve configuration, intake air flow characteristics, fuel injection strategy, injector mounting and operating conditions.

Combustion Characteristics of a Single-Cylinder Engine Equipped with Gasoline and Ethanol Dual-Fuel Systems

The requirement of reduced emissions and improved fuel economy led the introduction of direct-injection (DI) spark-ignited (SI) engines. Dual-fuel injection system (direct-injection and port-fuel-injection (PFI)) was also used to improve engine performance at high load and speed. Ethanol is one of the several alternative transportation fuels considered for replacing fossil fuels such as gasoline and diesel. Ethanol offers high octane quality but with lower energy density than fossil fuels. This paper presents the combustion characteristics of a single cylinder dual-fuel injection SI engine with the following fueling cases: a) gasoline for PFI and DI, b) PFI gasoline and DI ethanol, and c) PFI ethanol and DI gasoline. For this study, the DI fueling portion varied from 0 to 100 percentage of the total fueling over different engine operational conditions while the engine air-to-fuel ratio remained at a constant level. It was shown in all cases that the IMEP (indicated mean effective pressure) decreases by as much as 11% as DI fueling percentage increases, except in case b) where the IMEP increases by 2% at light load. The combustion burn duration increases significantly at light load as DI fueling percentage increases, but only moderately at WOT (wide open throttle). In addition, the percentage of the ethanol in the total fueling plays a dominant role in affecting the combustion characteristics at light load; but at heavy load (WOT), the DI fueling percentage becomes an important parameter, regardless of the percentage of ethanol content in the fuel.

A study of fuel impingement analysis on in-cylinder surfaces in a direct-injection spark-ignition engine with gasoline and ethanol-gasoline blended fuels

An experimental study is performed to investigate the fuel impingement on cylinder walls and piston top inside a directinjection spark-ignition engine with optical access to the cylinder. Three different fuels, namely, E85, E50 and gasoline are used in this work. E85 represents a blend of 85 percent ethanol and 15 percent gasoline by volume. Experiments are performed at different load conditions with the engine speeds of 1500 and 2000 rpm. Two types of fuel injectors are 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. In addition, the effects of split injection are also presented and compared with the similar cases of single injection by maintaining the same amount of fuel for the stoichiometric condition. Novel image processing algorithms are developed to analyze the fuel impingement quantitatively on cylinder walls and piston top inside the engine cylinder. Qualitative details of spray tip penetration are also presented to reveal the effects of ethanol fuels compared to that of gasoline. It is found that the split injection is an effective way to reduce the overall fuel impingement on in-cylinder surfaces. No significant difference is observed on fuel spray pattern when gasoline is compared with E50 and E85. However, spray tip penetration is slightly higher with gasoline than that of ethanol fuels. Results also show that the wall impingement is higher with gasoline compared to ethanol fuels. INTRODUCTION Improvement in fuel efficiency and reduction in exhaust emissions are the main goals behind the new developments in internal combustion (IC) engines. The concept of directinjection spark-ignition (DISI) engine has the potential to achieve such goals. In this technology, fuel is directly injected into the engine cylinder, which offers great flexibility to control the fuel injection timing, its duration and the number of injections. Note that the fuel-air mixture preparation in the combustion chamber is one of the key factors that influences the in-cylinder combustion characteristics and hence the engine performance (Hung et al., 2007). Therefore, optimizing the fuel-air mixture homogeneity is an important parameter for the engine designers. In general, a homogeneous fuel-air mixture is achieved by injecting the fuel during the intake stroke. However, due to in-cylinder injection and higher injection pressures, the fuel impingement levels on in-cylinder surfaces in DISI engines are typically higher than those in port-fuel injection (PFI) engines (Pereira et al., 2007). This results in an increase in the levels of un-burned hydrocarbons and smoke emissions, which reduces the potential fuel economy benefits associated with the direct-injection engines. Therefore, it is important to control the fuel injection timing precisely in order to minimize the fuel impingement on incylinder surfaces. Several studies have been reported on fuel spray pattern visualization and its influence on mixture formation inside the cylinder of direct-injection systems. Grimaldi et al. (2000) A Study of Fuel Impingement Analysis on InCylinder Surfaces in a Direct-Injection SparkIgnition Engine with Gasoline and Ethanol-Gasoline Blended Fuels 2010-01-2153 Published 10/25/2010

Fast mass-fraction-burned calculation using the net pressure method for real-time applications

Abstract The mass fraction burned (MFB) is determined from the analysis of measured in-cylinder pressure data. In this paper, a net pressure method (model 2) is used to evaluate the MFB curves at different load conditions (3.3 bar indicated mean effective pressure and wide-open throttle) using a constant polytropic index. Results are compared with the well-known Rassweiler—Withrow method (model 1), which is a linear model for the polytropic index. Model 2 showed good agreement with model 1 at high-load conditions; however, it predicts slower combustion at part-load conditions than that of model 1. It is found that the proper selection of the polytropic index n and the determination of the end of combustion are the important parameters for calculating the MFB curves using model 2. The modified form of model 2 compares well with the results of model 1 for evaluating the MFB at part-load conditions. The MFB results of the modified form (of model 2) also show good agreement with model 1 at high-load conditions. Model 2 has an advantage that the data-processing time is short enough to allow for online processing.