Water Addition in Diesel Engine Intake for NOx Reduction: Comparison of Modeling and Experiments

Reduction in emissions, especially NOx has been the main study of various engine researchers in the light of stringent emission norms. To reduce the time and cost involved in testing these technologies, engine thermodynamic cycle predictive tools are used. The present work uses one such predictive tool (GT Power from Gamma Technologies) for predicting the influence of water addition in a turbocharged 6-cylinder diesel engine intake on engine performance and NOx emissions. The experiments for comparison with modeling included the introduction of liquid water in the engine intake stream, between the compressor and intercooler ranging from 0 to 100% of fuel flow rate. NOx emission reduced linearly with water addition with reduction of 63% with less than 1% penalty on fuel efficiency at 100% water addition. The GT Power model predicted the performance within 5% of experimental data and NOx emission within 10% of the experiments.

Ignition System Designed to Extend the Plug Life, and the Lean Limit in a Natural Gas Engine

An ignition system that is based on the alternating (AC) rather than the traditional direct (DC) current in the spark plug discharge has been developed at the Caterpillar Technical Center. This system can generate a long duration discharge with controllable power. It is believed that such an ignition system can provide both a leaner operating limit and a longer spark plug life than a traditional DC system due to the long discharge duration and the low discharge power. The AC ignition system has successfully been tested on a Caterpillar single cylinder G3500 natural gas engine to determine the effects on the engine performance, combustion characteristics and emissions. The test results indicate that while the AC ignition system has only a small impact on engine performance (with respect to a traditional DC system), it does extend the lean limit with lower NOx emissions. Evidences also show the potential of reduce spark plug electrode erosions from the low breakdown and sustaining discharge powers from the AC ignition system. This paper summarizes the prototype design and engine demonstration results of the AC ignition system.

Mechanical Validation: An Integral Part of Medium Speed Diesel Engine Development

A comprehensive mechanical testing program was part of the development of the Diesel engine for the GEVO locomotive family. The test program has been developed under consideration of the demands of a railroad application. The program included both fired engine and component rig testing. Component rig tests were used to validate major components early in the design stage. Engine testing included measurements to validate the CAE models and allow detailed experimental development of components and subsystems. Several endurance runs have proven the reliability of the new engine.

Missing Combustion Diagnosis: Distinguishing Between Misfire and Misfuel

On-Board Diagnostics (OBD) regulations impose missing combustions detection within a wide portion of the engine operating range. Missing combustions can be caused either by ignition (misfire) or injection (misfuel) system failures. Missing combustions can damage the catalyst and cause abrupt pollutants increases (especially HC), but misfuels are not as detrimental as misfires, both from the emissions and the after treatment system life point of view. It would be important for the Electronic Control Unit (ECU) to be informed not only about the fault event, but also about its type, for the purpose of setting the right recovery strategy. The aim of this paper is to analyze missing combustion phenomena, in order to find out if a fault recognition strategy able to distinguish between misfire and misfuel can be setup. Different approaches can be found in the literature to diagnose missing combustions: many of them are based on the speed signal analysis, both in time and frequency domains, others use the knock accelerometer signal, or the exhaust manifold pressure information. A Universal Exhaust Gas Oxygen (UEGO) sensor can also be used. Usually diagnosis methodologies consist in observing signals perturbations subsequent to the malfunction event. Observable consequences of missing combustions are, for example, a sudden lack of indicated torque, causing vibrations and speed fluctuations, an increasing in exhaust gases Oxygen content, anomalous exhaust pressure ripples, etc. Many phenomena interact influencing in different ways the engine behavior, during and after the fault event: their effect can depend on the fault cause, thus helping the recognition. The first combustion taking place in the faulty cylinder after a misfire (post-misfiring cycle) usually leads to higher indicated pressure and torque levels if compared to standard values for the same operating conditions, while the same cannot be said for the post-misfueling combustion. On the other side, Air-Fuel Ratio (AFR) assumes different trends during the misfiring and post-misfiring cycles, with respect to misfueling and post-misfueling cycles. A 4 cylinders 1.2 liters spark ignition port injected engine, equipped with a programmable Electronic Control Unit (ECU) has been tested on the test bench, inducing both misfires and misfuels, over a wide engine operating range, while monitoring the engine faulty behavior. Misfire and misfuel-related phenomena have been analyzed showing their “signature” on indicated pressure and torque, engine speed and Air-Fuel Ratio measured signals, in order to define the most reliable recognition strategy.

Computational Study of Fuel Injection in a Large-Bore Gas Engine

Emission controls in stationary gas engines have required significant modifications to the fuel injection and combustion processes. One approach has been the use of high-pressure fuel injection to improve fuel-air mixing. The objective of this study is to simulate numerically the injection of gaseous fuel at high pressure in a large-bore two-stroke engine. Existing combustion chamber geometry is modeled together with proposed valve geometry. The StarCD® fluid dynamics code is used for the simulations, using appropriate turbulence models. High-pressure injection of up to 500 psig methane into cylinder air initially at 25 psig is simulated with the valve opened instantaneously and piston position frozen at the 60 degrees ABDC position. Fuel flow rate across the valve throat varies with the instantaneous pressure but attains a steady state in approximately 22 ms. As expected with the throat shape and pressures, the flow becomes supersonic past the choked valve gap, but returns to a subsonic state upon deflection by a shroud that successfully directs the flow more centrally. This indicates the need for careful shroud design to direct the flow without significant deceleration. Pressures below 300 psig were not effective with the proposed valve geometry. A persistent re-circulation zone is observed immediately below the valve, where it does not help promote mixing.

Experimentally Determined Port Discharge Coefficients From Large-Bore Reciprocating Engines

This paper describes the collection and analysis of discharge coefficients from the ports of large-bore two-stroke cycle engines. The literature includes some information on discharge coefficients from very small ports. The literature was found to not include data collected from very large ports, such is in Cooper, Clark, and Worthington two-stroke cycle engines. The methodology was to construct and then use a flow bench that was sized for large-bore engine cylinder liners. The flow bench is designed to experimentally determine the discharge coefficients of large bore engine ports. The discharge coefficients are an integral part of determining the air flow rate through an engine, and in modeling and predicting the airflow through an engine system. This information can be used by designers to better match turbochargers and aftercoolers to engines. Large bore engine cylinders are typically are 35–56 cm (14–22 in.) in diameter, and have power outputs ranging 745–3730 kW (1,000–6,000 hp). In general, the majority of these engines were built in the 1940–1950’s. The importance of predicting the airflow rate through these engines has become paramount due to increasingly stringent EPA emission regulations. The data shows that there is a vast difference between the discharge coefficients of the three primary engines used in the natural gas industry.

Thermophysical Properties of Working Substance and Heat Transfer in a Hydrogen Combustion Engine

Hydrogen is a clean alternative to fossil fuels for internal combustion engines and can be easily used in spark-ignition engines. However, the characteristics of the engines fueled with hydrogen are largely different from those with conventional hydrocarbon fuels. A higher burning velocity and a shorter quenching distance for hydrogen as compared with hydrocarbons bring a higher degree of constant volume and a larger heat transfer from the burning gas to the combustion chamber wall of the engines. Because of the large heat loss, the thermal efficiency of an engine fueled with hydrogen is sometimes lower than that with hydrocarbons. Therefore, the analysis and the reduction of the heat loss are crucial for the efficient utilization of hydrogen in internal combustion engines. The empirical correlations to describe the total heat transferred from the burning gas to the combustion chamber walls are often used to calculate the heat loss in internal combustion engines. However, the previous research by one of the authors has shown that the widely used heat transfer correlations cannot be properly applied to the hydrogen combustion even with adjusting the constants in them. For this background, this research analyzes the relationship between characteristics of thermophysical properties of working substance and heat transfer to the wall in a spark-ignition engine fueled with hydrogen.

Preliminary Energy-Efficiency Analyses of an Active-Flow Aftertreatment System for Lean-Burn IC Engines

Exhaust purification for lean-burn internal combustion engines has been impaired by the relatively low temperature of the exhaust that makes conventional passive aftertreatment schemes less energy-efficient in oxidation/regeneration. To tackle such adversaries, an active-flow control scheme, reversal-flow control, is outlined and analyzed in this paper. Preliminary energy-efficiency analyses are performed with different gas flow rate, flow reversal frequency, and monolith-solid properties. Simulation results indicate that through active thermal management the supplemental energy consumption can be drastically reduced, which is also supported by previous empirical studies.

Instantaneous Engine Speed Analysis for Cylinder Isolation in Multiple Misfire Events

Misfire detection is a subject that has been deep studied during the last years and many methodologies have been developed for this purpose. Affordably detecting the misfire event and isolating the cylinder where the missing combustion took place can be considered a solved problem for engines with a limited number of cylinders. Misfire detection and in particular cylinder isolation is still challenging for engine operating conditions at very low load and high engine speed, for engines with a high number of cylinders, or when more than one misfire event is present within the same engine cycle (multiple misfire). In particular this last malfunctioning condition is very challenging, and its detection is enforced by the international regulations without requiring cylinder isolation, but only the number of misfiring cylinders. Many methodologies have been developed in the past based on the analysis of the instantaneous engine speed. The missing combustion effect on this signal is anyway very low when the number of cylinders is high and for engine operating conditions at low engine speed, giving rise to misdetection or false alarms as already mentioned. In addition when a misfire event takes place a torsional vibration is excited and shows up in the instantaneous engine speed waveform. If a multiple misfire occurs this torsional vibration is excited more than once in a very short time interval. The interaction among these successive vibrations can further generate false alarms or misdetection, and an increased complexity when dealing with cylinder isolation is necessary. The approach here presented permits enhancing existing misfire detection methods through optimized algorithm that allows correctly isolating the multiple misfiring cylinders over the entire engine operating range. This has been obtained by proper identifying the effect of the torsional vibration over the instantaneous engine speed. The identified waveform has been then used to filter out the torsional vibration effects in order to enlighten the effects of the missing combustions. In addition a proper instantaneous engine speed windowing has been introduced in order to increase the detection signal to noise ratio over the whole engine operating range. The integration of these two signal processing techniques has proven to be very effective on the engine investigated in this study, and it is easily extendible to other engine architectures. Particular care has been devoted to satisfy on-board implementation requirements in terms of memory allocation and computational power. The tests have been conducted on an L4 1.2 liter spark ignition engine mounted in a test cell. In-cylinder pressure signals have been acquired in order to validate the methodology here developed.

The Advanced Injection Low Pilot Ignited Natural Gas Engine: A Combustion Analysis

The Advanced Low Pilot Ignited Natural Gas (ALPING) engine is proposed as an alternative to diesel and conventional dual fuel engines. Experimental results from full load operation at a constant speed of 1700 rev/min are presented in this paper. The potential of the ALPING engine is realized in reduced NOx emissions (less than 0.2 g/kWh) at all loads accompanied by fuel conversion efficiencies comparable to straight diesel operation. Some problems at advanced injection timings are recognized in high unburned hydrocarbon (HC) emissions (25 g/kWh), poor engine stability reflected by high COVimep (about 6 percent), and tendency to knock. This paper focuses on the combustion aspects of low pilot ignited natural gas engines with particular emphasis on advanced injection timings (45°–60°BTDC).