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Technical Paper

Evaluation of Six Natural Gas Combustion Systems for LNG Locomotive Applications

An experimental program to develop a practical natural gas-fueled locomotive engine was conducted. Six natural gas-fueled combustion systems for an EMD 710-type locomotive engine were developed and tested. The six systems were evaluated in terms of NOx and CO emissions, thermal efficiency, knock tolerance, and other practical considerations. Each combustion system was tested at Notch 5, 100-percent load, Notch 8, 80-percent load, and Notch 8, 100-percent load conditions. In general, all of the technologies produced significantly lower NOx emissions than the baseline diesel engine. Based on the results of the tests and other analyses, a late cycle, high-injection pressure (LaCHIP) combustion system, using a diesel pilot-ignited, late cycle injection of natural gas with a Diesel-type combustion process, was determined to provide the most practical combustion system for a natural gas-fueled, EMD 710-powered locomotive.
Technical Paper

Diesel Engine Flame Photographs With High Pressure Injection

The effect of high pressure injection (using an accumulator type unit injector with peak injection pressure of approximately 20,000 psi, having a decreasing injection rate profile) on combustion was studied. Combustion results were obtained using a DDA Series 3–53 diesel engine with both conventional analysis techniques and high speed photography. Diesel No. 2 fuel and a low viscosity - high volatility fuel, similar to gasoline were used in the study. Results were compared against baseline data obtained with standard injectors. Some of the characteristics of high pressure injection used with Diesel No. 2 fuel include: substantially improved ignition, shorter ignition delay, and higher pressure rise. Under heavy load - high speed conditions, greater smokemeter readings were achieved with the high pressure injection system with Diesel No. 2 fuel. Higher flame speeds and hence, greater resistance to knock were observed with the high volatility low cetane fuel.
Technical Paper

Expanding Diesel Engine Cetane Limits through Staged Injection

Interest in alternative diesel fuels has led to consideration of various types of poor ignition quality products, such as a broad cut fuel or a synthetic fuel/DF-2 blend. Attempts were made to expand the cetane number tolerance limit of an EMD 567B medium-speed diesel engine through staged injection to permit operation on such fuels. A small portion of the fuel was injected early in the cycle to act as a pilot for the main fuel charge. Both pilot and main charges were the same fuel. Knocking was eliminated on fuels with cetane numbers as low as 17 at the standard 16:1 compression ratio. Attempts to operate on methanol at 20:1 failed, but such operation may be feasible with further modifications.
Technical Paper

Use of Alcohol-in-Diesel Fuel Emulsions and Solutions in a Medium-Speed Diesel Engine

The use of alcohol as a supplemental fuel for a medium-speed diesel engine was investigated using a two-cylinder, two-stroke test engine. Both stabilized and unstabilized emulsions of methanol-in-diesel fuel and ethanol-in-diesel fuel were tested. Also, anhydrous ethanol/diesel fuel solutions were evaluated. Maximum alcohol content of the emulsions and solutions was limited by engine knocking due to a reduction in fuel cetane number. Engine power and thermal efficiency were slightly below baseline diesel fuel levels in the high and mid-speed ranges, but were somewhat improved at low speeds during tests of the unstabilized emulsions and the ethanol solutions. However, thermal efficiency of the stabilized emulsions fell below baseline levels at virtually all conditions.
Technical Paper

Octane Response of Premium-Recommended Vehicles

A higher octane quality fuel used in premium-recommended vehicles has the potential for delivering better acceleration and power. Octane number is a standard measure for the anti-knock quality of a gasoline fuel. A higher octane number fuel can withstand more compression before detonation (or knock). Higher compression ratios directly correlate with engine power and thermodynamic efficiency. Hence engines that are designed for higher octane or premium grade fuels should typically develop higher power by extracting more from the calorific value of the fuel. However, in the case of premium-recommended vehicle models that are designed to run even on lower octane fuels, the extent of performance benefits of using premium grade higher octane fuels can be deciphered via vehicle testing. In this regard, two gasoline fuels with anti-knock index values (AKI) of 87 and 91 respectively were compared in five premium-recommended vehicles for acceleration and power benefits.
Technical Paper

Blend Ratio Optimization of Fuels Containing Gasoline Blendstock, Ethanol, and Higher Alcohols (C3-C6): Part II - Blend Properties and Target Value Sensitivity

Higher carbon number alcohols offer an opportunity to meet the Renewable Fuel Standard (RFS2) and improve the energy content, petroleum displacement, and/or knock resistance of gasoline-alcohol blends from traditional ethanol blends such as E10 while maintaining desired and regulated fuel properties. Part II of this paper builds upon the alcohol selection, fuel implementation scenarios, criteria target values, and property prediction methodologies detailed in Part I. For each scenario, optimization schemes include maximizing energy content, knock resistance, or petroleum displacement. Optimum blend composition is very sensitive to energy content, knock resistance, vapor pressure, and oxygen content criteria target values. Iso-propanol is favored in both scenarios' suitable blends because of its high RON value.
Technical Paper

Blend Ratio Optimization of Fuels Containing Gasoline Blendstock, Ethanol, and Higher Alcohols (C3-C6): Part I - Methodology and Scenario Definition

The U.S. Renewable Fuel Standard (RFS2) requires an increase in the use of advanced biofuels up to 36 billion gallons by 2022. Longer chain alcohols, in addition to cellulosic ethanol and synthetic biofuels, could be used to meet this demand while adhering to the RFS2 corn-based ethanol limitation. Higher carbon number alcohols can be utilized to improve the energy content, knock resistance, and/or petroleum displacement of gasoline-alcohol blends compared to traditional ethanol blends such as E10 while maintaining desired and regulated fuel properties. Part I of this paper focuses on the development of scenarios by which to compare higher alcohol fuel blends to traditional ethanol blends. It also details the implementation of fuel property prediction methods adapted from literature. Possible combinations of eight alcohols mixed with a gasoline blendstock were calculated and the properties of the theoretical fuel blends were predicted.
Technical Paper

Impact of Operating Parameters on Ignition System Energy Consumption

The use of cooled EGR in gasoline engines improves the fuel efficiency of the engine through a variety of mechanisms, including improving the charge properties (e.g. the ratio of specific heats), reducing knock and enabling higher compression ratio operation and, at part loads conditions in particular, reducing pumping work. One of the limiting factors on the level of improvement from cooled EGR is the ability of the ignition system to ignite a dilute mixture and maintain engine stability. Previous work from SwRI has shown that, by increasing the ignition duration and using a continuous discharge ignition system, an improved ignition system can substantially increase the EGR tolerance of an engine [1, 2]. This improvement comes at a cost, however, of increased ignition system energy requirements and a potential decrease in spark plug durability. This work examines the impact of engine operating parameters on the ignition energy requirements under high dilution operation.
Technical Paper

Transient Control of a Dedicated EGR Engine

Southwest Research Institute (SwRI) has successfully demonstrated the cooled EGR concept via the High Efficiency Dilute Gasoline Engine (HEDGE) consortium. Dilution of intake charge provides three significant benefits - (1) Better Cycle Efficiency (2) Knock Resistance and (3) Lower NOx/PM Emissions. But EGR dilution also poses challenges in terms of combustion stability, condensation and power density. The Dedicated EGR (D-EGR) concept brings back some of the stability lost due to EGR dilution by introducing reformates such as CO and H2 into the intake charge. Control of air, EGR, fuel, and ignition remains a challenge to realizing the aforementioned benefits without sacrificing performance and drivability. This paper addresses the DEGR solution from a controls standpoint. SwRI has been developing a unified framework for controlling a generic combustion engine (gasoline, diesel, dual-fuel natural gas etc.).
Technical Paper

Dual Fuel Combustion Study Using 3D CFD Tool

The current boom in natural gas from shale formations in the United States has reduced the price of natural gas to less than the price of petroleum fuels. Thus it is attractive to convert high horsepower diesel engines that use large quantities of fuel to dual fuel operation where a portion of the diesel fuel is replaced by natural gas. The substitution is limited by emissions of unburned natural gas and severe combustion phenomena such as auto-ignition or knock of the mixture and high rates of pressure rise during the ignition and early phase combustion of the diesel and natural gas-air mixture. In this work, the combustion process for dual fuel combustion was investigated using 3D CFD. The combustion process was modeled using detailed chemistry and a simulation domain sensitivity study was conducted to investigate the combustion to CFD geometry assumptions. A baseline model capturing the onset of knock was validated against experimental data from a heavy-duty dual-fuel engine.
Technical Paper

Spark Ignited Direct Injection Natural Gas Combustion in a Heavy Duty Single Cylinder Test Engine - Start of Injection and Spark Timing Effects

The increased availability of natural gas (NG) in the United States (US), and its relatively low cost compared to diesel fuel has heightened interest in the conversion of medium duty (MD) and heavy duty (HD) engines to NG fueled combustion systems. The aim is to realize fuel cost savings and reduce harmful emissions, while maintaining durability. This is a potential path to help the US reduce dependence on crude oil. Traditionally, port-fuel injection (PFI) or premixed NG spark-ignited (SI) combustion systems have been used for MD and HD engines with widespread use in the US and Europe; however, this technology exhibits poor cycle efficiency and is load limited due to knock phenomenon. Direct Injection of NG during the compression stroke promises to deliver improved thermal efficiency by avoiding excessive premixing and extending the lean limits which helps to extend the knock limit.
Technical Paper

Impact of Swirl Ratio on Combustion Performance of a Non-Pent Roof Combustion Chamber Engine

In response to the sensitivity to diesel aftertreatment costs in the medium duty market, a John Deere 4045 was converted to burn gasoline with high levels of EGR. This presented some unique challenges not seen in light duty gasoline engines as the flat head and diesel adapted ports do not provide optimum in-cylinder turbulence. As the bore size increases, there is more opportunity for knock or incomplete combustion to occur. Also, the high dilution used to reduce knock slows the burn rates. In order to speed up the burn rates, various levels of swirl were investigated. A four valve head with different levels of port masking showed that increasing the swirl ratio decreased the combustion duration, but ultimately ran into high pumping work required to generate the desired swirl. A two valve head was used to overcome the breathing issue seen in the four valve head with port masking.
Technical Paper

A High-Energy Continuous Discharge Ignition System for Dilute Engine Applications

SwRI has developed the DCO® ignition system, a unique continuous discharge system that allows for variable duration/energy events in SI engines. The system uses two coils connected by a diode and a multi-striking controller to generate a continuous current flow through the spark plug of variable duration. A previous publication demonstrated the ability of the DCO system to improve EGR tolerance using low energy coils. In this publication, the work is extended to high current (≻ 300 mA/high energy (≻ 200 mJ) coils and compared to several advanced ignition systems. The results from a 4-cylinder, MPI application demonstrate that the higher current/higher energy coils offer an improvement over the lower energy coils. The engine was tested at a variety of speed and load conditions operating at stoichiometric air-fuel ratios with gasoline and EGR dilution.
Technical Paper

Alternative Fuel Testing on a Port Fuel Injected LPL EGR and D-EGR® Engine

A turbocharged 2.0 L PFI engine was modified to operate in a low-pressure loop and Dedicated EGR (D-EGR®) engine configuration. Both engine architectures were operated with a low and high octane gasoline as well as three ethanol blends. The core of this study focused on examining combustion differences at part and high loads between the selected fuels and also the different engine configurations. Specifically, the impact of the fuels on combustion stability, burn rates, knock mitigation, required ignition energy, and efficiency were evaluated. The results showed that the knock resistance generally followed the octane rating of the fuel. At part loads, the burn rates, combustion stability, and EGR tolerance was marginally improved with the high ethanol blends. When combustion was not knock or stability limited, the efficiency differences between the fuels were negligible. The D-EGR engine was much less sensitive to fuel changes in terms of burn rates than the LPL EGR setup.
Technical Paper

Investigation of Combustion Knock Distribution in a Boosted Methane-Gasoline Blended Fueled SI Engine

The characteristics of combustion knock metrics over a number of engine cycles can be an essential reference for knock detection and control in internal combustion engines. In a Spark-Ignition (SI) engine, the stochastic nature of combustion knock has been shown to follow a log-normal distribution. However, this has been derived from experiments done with gasoline only and applicability of log-normal distribution to dual-fuel combustion knock has not been explored. To evaluate the effectiveness and accuracy of log-normal distributed knock model for methane-gasoline blended fuel, a sweep of methane-gasoline blend ratio was conducted at two different engine speeds. Experimental investigation was conducted on a single cylinder prototype SI engine equipped with two fuel systems: a direct injection (DI) system for gasoline and a port fuel injection (PFI) system for methane.
Technical Paper

Selective Interrupt and Control: An Open ECU Alternative

To enable the evaluation of off-calibration powertrain operation, a selective interrupt and control (SIC) test capability was developed as part of an EPA evaluation of a 1.6 L EcoBoost® engine. A control and data acquisition device sits between the stock powertrain controller and the engine; the device selectively passes through or modifies control signals while also simulating feedback signals. This paper describes the development process of SIC that enabled a test engineer to command off-calibration setpoints for intake and exhaust cam phasing as well as ignition timing without the need for an open ECU duplicating the stock calibration. Results are presented demonstrating the impact of ignition timing and cam phasing on engine efficiency. When coupled with combustion analysis and crank-domain data acquisition, this test configuration provides a complete picture of powertrain performance.
Technical Paper

The New BAIC High Efficiency Turbocharged Engine with LPL-EGR

The new Beijing Automotive Industry Corporation (BAIC) engine, an evolution of the 2.3L 4-cylinder turbocharged gasoline engine from Saab, was designed, built, and tested with close collaboration between BAIC Motor Powertrain Co., Ltd. and Southwest Research Institute (SwRI®). The upgraded engine was intended to achieve low fuel consumption and a good balance of high performance and compliance with Euro 6 emissions regulations. Low fuel consumption was achieved primarily through utilizing cooled low pressure loop exhaust gas recirculation (LPL-EGR) and dual independent cam phasers. Cooled LPL-EGR helped suppress engine knock and consequently allowed for increased compression ratio and improved thermal efficiency of the new engine. Dual independent cam phasers reduced engine pumping losses and helped increase low-speed torque. Additionally, the intake and exhaust systems were improved along with optimization of the combustion chamber design.
Technical Paper

Target Based Rapid Prototyping Control System for Engine Research

Today's advanced technology engines have a high content of electronic actuation requiring sophisticated real-time embedded software sensing and control. To enable research on such engines, a system with a flexible engine control unit (ECU) that can be rapidly configured and programmed is desired. Such a system is being used in the Advanced Internal Combustion Engine (AICE) Laboratories at Michigan Tech University (MTU) for research on a multi-cylinder spark-ignited gasoline, a high pressure common rail diesel and a single cylinder alternative fuels research engine. The system combines a production ECU with a software development system utilizing Mathworks Simulink/Stateflow © modeling tools. The interface in the Simulink modeling environment includes a library of modeling and interface blocks to the production Operating System (OS), Low Level Drivers (LLD) and CAN-based calibration tool.
Technical Paper

Analysis of Combustion Knock Metrics in Spark-Ignition Engines

Combustion knock detection and control in internal combustion engines continues to be an important feature in engine management systems. In spark-ignition engine applications, the frequency of occurrence of combustion knock and its intensity are controlled through a closed-looped feedback system to maintain knock at levels that do not cause engine damage or objectionable audible noise. Many methods for determination of the feedback signal for combustion knock in spark-ignition internal combustion engines have been employed with the most common technique being measurement of engine vibration using an accelerometer. With this technique single or multiple piezoelectric accelerometers are mounted on the engine and vibrations resulting from combustion knock and other sources are converted to electrical signals. These signals are input to the engine control unit and are processed to determine the signal strength during a period of crank-angle when combustion knock is expected.
Technical Paper

Effect of Reduced Boost Air Temperature on Knock Limited Brake Mean Effective Pressure (BMEP)

The effect of low temperature intake air on the knock limited brake mean effective pressure (BMEP) in a spark ignited natural gas engine is described in this paper. This work was conducted to demonstrate the feasibility of using the vaporization of liquefied natural gas (LNG) to reduce the intake air temperature of engines operating on LNG fuel. The effect on steady-state emissions and transient response are also reported. Three different intake air temperatures were tested and evaluated as to their impact upon engine performance and gaseous emissions output. The results of these tests are as follows. The reduced intake air temperature allowed for a 30.7% (501 kPa) increase in the knock-limited BMEP (comparing the 10°C (50°F) intake air results with the 54.4°C (130°F) results). Exhaust emissions were recorded at constant BMEP for varying intake air temperatures.