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Technical Paper

An Experimental Investigation of Diesel-Gasoline Blends Effects in a Direct-Injection Compression-Ignition Engine Operating in PCCI Conditions

2013-04-08
2013-01-1676
Compared to the gasoline engine, the diesel engine has the advantage of being more efficient and hence achieving a reduction of CO₂ levels. Unfortunately, particulate matter (PM) and nitrogen oxides (NOx) emissions from diesel engines are high. To overcome these drawbacks, several new combustion concepts have been developed, including the PCCI (Premixed Charge Compression Ignition) combustion mode. This strategy allows a simultaneous reduction of NOx and soot emissions through the reduction of local combustion temperatures and the enhancement of the fuel/air mixing. In spite of PCCI benefits, the concept is characterized by its high combustion noise levels. Currently, a promising way to improve the PCCI disadvantages is being investigated. It is related with the use of low cetane fuels such as gasoline and diesel-gasoline blends.
Technical Paper

Experimental Investigation of Close-Loop Control of HCCI Engine Using Dual Fuel Approach

2013-04-08
2013-01-1675
Homogeneous Charge Compression Ignition (HCCI) offers great promise for excellent fuel economy and extremely low emissions of NOx and PM. HCCI combustion lacks direct control on the "start of combustion" such as spark timing in SI engines and fuel injection timing in CI engines. Auto ignition of a homogeneous mixture is very sensitive to operating conditions of the engine. Even small variations of the load can change the timing from "too early" to "too late" combustion. Thus a fast combustion phasing control is required since it sets the performance limitation of the load control. Crank angle position for 50% heat release is used as combustion phasing feedback parameter. In this study, a dual-fuel approach is used to control combustion in a HCCI engine. This approach involves controlling the combustion heat release rate by adjusting fuel reactivity according to the conditions inside the cylinder. Two different octane fuels (methanol and n-heptane) are used for the study.
Technical Paper

Pressure Sensitivity of HCCI Auto-Ignition Temperature for Gasoline Surrogate Fuels

2013-04-08
2013-01-1669
An index to relate fuel properties to HCCI auto-ignition would be valuable to predict the performance of fuels in HCCI engines from their properties and composition. The indices for SI engines, the Research Octane Number (RON) and Motor Octane Number (MON) are known to be insufficient to explain the behavior of oxygenated fuels in an HCCI engine. One way to characterize a fuel is to use the Auto-Ignition Temperature (AIT). The AIT can be extracted from the pressure trace. Another potentially interesting parameter is the amount of Low Temperature Heat Release (LTHR) that is closely connected to the ignition properties of the fuel. A systematic study of fuels consisting of gasoline surrogate components of n-heptane, iso-octane, toluene, and ethanol was made. 21 fuels were prepared with RON values ranging from 67 to 97.
Technical Paper

Development of a Model-Based HCCI Control Strategy for an Engine with a Fully Variable Valve Train

2013-04-08
2013-01-1667
This paper discusses research activities at the Technische Universität München on the HCCI combustion process, focusing on the development of a model-based control concept with pressure indication. As a first step sensitivity analyses have been carried out to investigate influences of different injection strategies on the combustion and emission characteristics. An optimal injection strategy has been determined and reasonable control variables and ranges corresponding to this strategy were defined. Comprehensive steady-state measurements have been conducted to detect the engine characteristics. In order to limit the experimental effort, principles of DoE (Design of Experiments) have been used to define a methodological approach in the planning of the measurements. Afterwards a multiple-input multiple-output engine model including boundary models for input settings has been designed out of the measurement results.
Technical Paper

Study of Parallel Turbocompounding for Small Displacement Engines

2013-04-08
2013-01-1637
In order to reduce greenhouse gases and respect stringent pollutant emission regulations, the modern engine is increasingly required to incorporate energy recovery systems to enhance performance and increase efficiency. This paper deals with the exhaust energy recovery through turbocompounding. Both series and parallel turbocompounds are discussed. In the first part of the document, literature on turbocompounding is introduced. Then a simulation study carried on AMESim software, using a 2L Diesel engine model is presented. The parallel turbocompounding is simulated by expanding a part of the exhaust gases in a converging nozzle instead of the turbocharger turbine. The power produced is evaluated as a function of the pressure drop in case a turbine is mounted instead of the nozzle. A global study over the entire engine map is described, and two steady state points 2000 rpm, 8 bar and 3500 rpm, 7 bar are chosen.
Technical Paper

Optical Investigation on the Origin of Pre-Ignition in a Highly Boosted SI Engine Using Bio-Fuels

2013-04-08
2013-01-1636
Downsizing of highly-boosted spark-ignition (SI) engines is limited by pre-ignition, which may lead to extremely strong knocking and severe engine damage. Unfortunately, the concerning mechanisms are generally not yet fully understood, although several possible reasons have been suggested in previous research. The primary objective of the present paper is to investigate the influence of molecular bio-fuel structure on the locations of pre-ignition in a realistic, highly-charged SI engine at low speed by state-of-the-art optical measurements. The latter are conducted by using a high-sensitivity UV endoscope and an intensified high-speed camera. Two recently tested bio-fuels, namely tetrahydro-2-methylfuran (2-MTHF) and 2-methylfuran (2-MF), are investigated. Compared to conventional fuels, they have potential advantages in the well-to-tank balance. In addition, both neat ethanol and conventional gasoline are used as fuels.
Technical Paper

Laser Ignition of Single Cylinder Engine and Effects of Ignition Location

2013-04-08
2013-01-1631
Laser is emerging as a strong contender as an alternative ignition source for internal combustion (IC) engines. Short laser pulses of few nanoseconds duration delivered by a Q-switched laser are focused by a lens inside the engine cylinder containing combustible fuel-air mixture. If the peak intensity at the focal point exceeds threshold intensity level, breakdown of combustible gases occurs, which leads to plasma formation. If the energy of the spark generated by plasma is high enough, the mixture ignites. In this investigation, laser ignition (LI) was performed in a single cylinder engine at constant speed and wide open throttle conditions using CNG as fuel. Combustion behavior was recorded using a high speed data acquisition system. For laser ignition of the engine, a laser spark plug was designed and manufactured. Laser spark plug consists of combination of lenses and optical windows.
Technical Paper

Investigations of Ignition Processes Using High Frequency Ignition

2013-04-08
2013-01-1633
High frequency ignition (HFI) and conventional transistor coil ignition (TCI) were investigated with an optically accessible single-cylinder research engine to gain fundamental understanding of the chemical reactions taking place prior to the onset of combustion. Instead of generating heat in the gap of a conventional spark plug, a high frequency / high voltage electric field is employed in HFI to form chemical radicals. It is generated using a resonant circuit and sharp metallic tips placed in the combustion chamber. The setup is optimized to cause a so-called corona discharge in which highly energized channels (streamers) are created while avoiding a spark discharge. At a certain energy the number of ionized hydrocarbon molecules becomes sufficient to initiate self-sustained combustion. HFI enables engine operation with highly diluted (by air or EGR) gasoline-air mixtures or at high boost levels due to the lower voltage required.
Technical Paper

Experimental Study of a Pre-Chamber Jet Igniter in a Turbocharged Rotax 914 Aircraft Engine

2013-04-08
2013-01-1629
An experimental study is performed to investigate the possibility of relaxing the octane requirement of a Rotax 914 engine equipped with a pre-chamber jet ignition system. A pre-chamber jet igniter with no auxiliary fuel addition is designed to replace the spark plug in cylinder two of the test engine and is evaluated across engine speeds ranging from 2500 to 5500 RPM. Experiments are performed across both normally aspirated and boosted configurations using regular 87 AKI gasoline fuel. Normally aspirated results at 98 kPa manifold absolute pressure show a 7-10° burn rate improvement with the jet ignition combustion system. Tests to determine the maximum load at optimal combustion phasing (no spark retard) are then conducted by increasing boost pressure up to maximum knock limits.
Technical Paper

Impact of Ignition Energy Phasing and Spark Gap on Combustion in a Homogenous Direct Injection Gasoline SI Engine Near the EGR Limit

2013-04-08
2013-01-1630
For spark-ignition gasoline engines operating under the wide speed and load conditions required for light duty vehicles, ignition quality limits the ability to minimize fuel consumption and NOx emissions via dilution under light and part load conditions. In addition, during transients including tip-outs, high levels of dilution can occur for multiple combustion events before either the external exhaust gas can be adjusted and cleared from the intake or cam phasing can be adjusted for correct internal dilution. Further improvement and a thorough understanding of the impact of the ignition system on combustion near the dilution limit will enable reduced fuel consumption and robust transient operation. To determine and isolate the effects of multiple parameters, a variable output ignition system (VOIS) was developed and tested on a 3.5L turbocharged V6 homogeneous charge direct-injection gasoline engine with two spark plug gaps and three ignition settings.
Technical Paper

Optimization of a High Speed Gasoline Engine Using Genetic Algorithm

2013-04-08
2013-01-1626
In order to improve the torque of engine full load characteristics, especially for the engine torque at high speed, the genetic algorithm combining with the weighted sum method is adopted to optimize the performance of a high-speed gasoline engine. Firstly the simulation model is built by software GT-power. The simulated values are contrasted with the tested values at the same operating condition. The results show the correspondence of the calculated values with tested values. So it proves that the simulation model is reliable. According to the importance of torque at each speed, a corresponding weight coefficient is got. Using the weighted sum method to construct an evaluation function, the multi-objective optimization problem is transformed into a single one.
Technical Paper

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

2013-04-08
2013-01-1628
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

Analysis and Comparison of Typical Exhaust Gas Energy Recovery Bottoming Cycles

2013-04-08
2013-01-1648
Internal Combustion Engine (ICE) consumes approx. 2/3 of the oil in the word and 30-40% of the fuel combustion energy in an ICE is wasted in the form of thermal energy in the exhaust gas stream. Exhaust gas thermal energy recovery demonstrates a great potential for overall system thermal efficiency improvements and fuel saving. In this paper different exhaust gas energy recovery bottoming cycles have been analyzed and discussed based on fundamental thermodynamics theory. The typical bottoming cycles are classified into two categories: i.e. direct and indirect energy recovery bottoming cycles. New terms, i.e. Energy Recovery Efficiency (ERE), Energy Conversion Efficiency (ECE) and Overall Energy Conversion Efficiency (OECE) are proposed for the purposes of easier to analyze and easier to compare among the various bottoming cycles. Simplified formulas are derived to demonstrate the key design and operating parameters which define or limit the energy recovery potential.
Technical Paper

Numerical Simulation of Subcooled Nucleate Boiling in Cooling Jacket of IC Engine

2013-04-08
2013-01-1651
There has been a change in the thermal management of IC engines where engineers now like to harness the superior heat transfer rates available when limited and controlled nucleate boiling is used to remove heat from high temperature zones. Any flaws in the design of such systems, such as uncontrolled boiling that leads to Dry Out situation, can have an adverse effect on the cooling performance. A detailed engineering model of this process would allow engineers to weed out flawed designs early in the design process. In this paper, we proposed and validated a CFD model for this process. A CFD model is built using the commercial CFD solver ANSYS FLUENT. The mixture multiphase model is used to study subcooled nucleate boiling in IC engine cooling jackets. The departure of bubbles enhances heat transfer at walls, which is captured using the empirical correlation. Volumetric mass transfer is modeled using the inbuilt evaporation-condensation model.
Technical Paper

Testing a 50kW ORC at Different Heating and Cooling Source Conditions to Map the Performance Characteristics

2013-04-08
2013-01-1649
In 2007 the electrical power consumption of 180 rural Alaska villages was 370,000 MW-h, generated using isolated diesel gensets. From a stationary diesel engine considerable amount of heat energy at an elevated temperature is released into the atmosphere from engine jacket liquid and exhaust gases. In rural Alaska, due to the infrastructure, economic impact and needs of the villages, many of village gensets may not be appropriate for applying heat recovery for the purposes other than electrical power generation. Other appropriate types of heat recovery applications in Alaska may include desalination, refrigeration, and district heating. Also due to the varying sizes and electrical loads of most of the diesel gensets (from 100 kw to 1 MW); small-sized heat recovery power systems (80 kW or less) are preferred instead of industrial scale systems.
Technical Paper

Experimental Validation of a Dynamic Waste Heat Recovery System Model for Control Purposes

2013-04-08
2013-01-1647
This paper presents the identification and validation of a dynamic Waste Heat Recovery (WHR) system model. Driven by upcoming CO₂ emission targets and increasing fuel costs, engine exhaust gas heat utilization has recently attracted much attention to improve fuel efficiency, especially for heavy-duty automotive applications. In this study, we focus on a Euro-VI heavy-duty diesel engine, which is equipped with a Waste Heat Recovery system based on an Organic Rankine Cycle. The applied model, which combines first principle modeling with stationary component models, covers the two-phase flow behavior and the effect of control inputs. Furthermore, it describes the interaction with the engine on both gas and drivetrain side. Using engine dynamometer measurements, an optimal fit of unknown model parameters is determined for stationary operating points.
Technical Paper

Exhaust Phases in a DI Diesel Engine Based on Instantaneous Cyclic Heat Transfer Experimental Data

2013-04-08
2013-01-1646
In the present paper a new method is proposed for the analysis of the two main phases of the engine exhaust stroke blowdown and displacement. The method is based on the processing of fast-response experimental temperatures obtained from the exhaust manifold wall during the engine cycle. A novel experimental installation has been developed, which separates the engine transient temperature signals into two groups, namely the long- and the short- term response ones. This has been achieved by processing the respective signals acquired from two independent data acquisition systems. Furthermore, a new pre-amplification unit for fast response thermocouples, appropriate heat flux sensors and an innovative, object-oriented, control code for fast data acquisition have been designed and applied. For the experimental procedure a direct injection (DI), air-cooled diesel engine is used.
Technical Paper

Additional Power Generation from the Exhaust Gas of Diesel Engine by Bottoming Rankine Cycle

2013-04-08
2013-01-1639
Exhaust gases from diesel engines can be an adequate source of energy to run a bottoming Rankine cycle to increase the overall efficiency of the engine as it contains a significant portion of input energy. In this research, an automotive diesel engine was tested to estimate the available energy in the exhaust gas. Shell and tube heat exchangers were used to extract the heat from the exhaust gas and the performance of the two shell and tube heat exchangers were investigated with parallel and counter flow arrangements using water as the working fluid. The results obtained were below satisfactory as these heat exchangers were purchased from the marketplace and not optimized for this particular application. Thus attempts were made to optimize the design of the heat exchanger by computer simulation using the available experimental data.
Technical Paper

Design and Simulations of an Enhanced and Cost Effective Engine Split Cooling Concept

2013-04-08
2013-01-1640
The ongoing global trends in engine downsizing and continuous need for higher engine specific output require more heat to be transferred out of the engine and into the radiator. This higher heat rejection necessitates higher coolant flow rate which is often accompanied with higher water pump power consumption and increased coolant circuit's cavitations risk. An enhanced split cooling concept is proposed to overcome the stated limitations with more efficient and effective coolant distributions to the cylinder head and cylinder block. The proposed concept also enables the cylinder head to run cooler than the cylinder block without the need for additional thermostat or water pump. The temperature differences are achievable by optimizing the coolant flow rates going through the cylinder head and cylinder block using both the 1D and 3D simulation packages.
Technical Paper

The Free Piston Linear Generator - Development of an Innovative, Compact, Highly Efficient Range-Extender Module

2013-04-08
2013-01-1727
The present paper introduces the Free Piston Linear Generator (FPLG) - a compact electricity generation unit, which is being developed at the German Aerospace Center (DLR). It is designed as a free-piston combustion engine with integrated linear generator. This combination allows for highly efficient conversion of the chemical energy stored in a fuel to electrical energy. By combining a two stroke combustion chamber, a linear alternator and an adjustable gas spring the engine design results in a compact package. In comparison to conventional combustion engines, additional degrees of freedom are available for controlling the combustion process. In this context efficiency advantages are expected due to the missing mechanical link to a crank which leads to flexibility in terms of stroke and compression ratio. Applied as a range-extender-unit, the system provides additional electric energy to electric vehicles in case of discharged batteries.
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