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Technical Paper

Improvement of Premixed Compression Ignition Combustion using Various Injector Configurations

2011-04-12
2011-01-1357
Premixed compression ignition (PCI) combustion was implemented using advanced injection strategy and exhaust gas recirculation in a direct-injection single-cylinder diesel engine. The injection timing swept experiment using a baseline injector, which had an injection angle of 146° and 8 nozzle holes, obtained three types of combustion regime: conventional diesel combustion for an injection timing of 10° CA (crank angle) BTDC (before top dead center), PCI combustion for an injection timing of 40° CA BTDC and homogeneous charge compression ignition (HCCI) combustion for an injection timing of 80° CA BTDC. PCI combustion can be verified by burn duration analysis. The burn duration, which was defined as the period from 10% to 90% of the accumulated heat release, was very short in PCI combustion but not in the others. PCI combustion with an injection timing of 40° CA BTDC was achieved in a range of an exhaust gas recirculation (EGR) rate from 0% to around 40%.
Technical Paper

Mode Transition between Low Temperature Combustion and Conventional Combustion with EGR and Injection Modulation in a Diesel Engine

2011-04-12
2011-01-1389
Mode transition between low temperature combustion and conventional combustion was investigated in a direct injection diesel engine. Low temperature diesel combustion was realized by means of high exhaust gas recirculation rate (69~73%) and early injection timing (-28~ -16 crank angle degree after top dead center) compared with those (20% exhaust gas recirculation rate and -8 crank angle degree after top dead center) of conventional combustion. Tests were carried out at different engine speeds and injection pressures. Exhaust gas recirculation rate was changed transiently by controlling each throttle angle for fresh air and exhaust gas recirculation to implement mode transition. Various durations for throttle transition were applied to investigate the effect of speed change of exhaust gas recirculation rate on the characteristics of mode transition.
Journal Article

Evaluation of Diesel Oxidation Catalyst Conversion of Hydrocarbons and Particulate Matter from Premixed Low Temperature Combustion of Biodiesel

2011-04-12
2011-01-1186
Premixed low temperature combustion (LTC) in diesel engines simultaneously reduces soot and NOx at the expense of increased hydrocarbon (HC) and CO emissions. The use of biodiesel in the LTC regime has been shown to produce lower HC emissions than petroleum diesel; however, unburned methyl esters from biodiesel are more susceptible to particulate matter (PM) formation following atmospheric dilution due to their low volatility. In this study, the efficacy of a production-type diesel oxidation catalyst (DOC) for the conversion of light hydrocarbons species and heavier, semi-volatile species like those in unburned fuel is examined. Experimental data were taken from a high speed direct-injection diesel engine operating in a mid-load, late injection partially premixed LTC mode on ultra-low sulfur diesel (ULSD) and neat soy-based biodiesel (B100). Gaseous emissions were recorded using a conventional suite of analyzers and individual light HCs were measured using an FT-IR analyzer.
Technical Paper

Bridging the Gap between HCCI and SI: Spark-Assisted Compression Ignition

2011-04-12
2011-01-1179
Homogeneous charge compression ignition (HCCI) has received much attention in recent years due to its ability to reduce both fuel consumption and NO emissions compared to normal spark-ignited (SI) combustion. However, due to the limited operating range of HCCI, production feasible engines will need to employ a combination of combustion strategies, such as stoichiometric SI combustion at high loads and leaner burn spark-assisted compression ignition (SACI) and HCCI at intermediate and low loads. The goal of this study was to extend the high load limit of HCCI into the SACI region while maintaining a stoichiometric equivalence ratio. Experiments were conducted on a single-cylinder research engine with fully flexible valve actuation. In-cylinder pressure rise rates and combustion stability were controlled using cooled external EGR, spark assist, and negative valve overlap. Several engine loads within the SACI regime were investigated.
Technical Paper

Effects of Single and Double Post Injections on Diesel PCCI Combustion

2013-03-25
2013-01-0010
In this study, single and double post injections were applied to diesel premixed charge compression ignition (PCCI) combustion to overcome the drawbacks those are high level of hydrocarbons (HC) and carbon monoxide (CO) emissions in a single-cylinder direct-injection diesel engine. The operating conditions including engine speed and total injection quantity were 1200 rpm and 12 mg/cycle, which are the representative of low engine speed and low load. The main injection timing of diesel PCCI combustion was set to 28 crank angle degree before top dead center (CAD BTDC). This main injection timing showed 32% lower level of nitric oxides (NOx) level and 8 CAD longer ignition delay than those of conventional diesel combustion. However, the levels of HC and CO were 2.7 and 3 times higher than those of conventional diesel combustion due to over-lean mixture and wall wetting of fuel.
Technical Paper

Diesel Knock Visualization and Frequency Analysis of Premixed Charge Compression Ignition Combustion with a Narrow Injection Angle

2013-04-08
2013-01-0906
In this study, premixed charge compression ignition (PCCI) combustion was implemented using an injector that had a narrow injection angle of 70° and a moderately early injection timing of -40° crank angle after top dead center (CA ATDC). In-cylinder pressure measurements and high-speed direct imaging of the flame were performed in an optically accessible single-cylinder diesel engine. Frequency analysis of the acquired in-cylinder pressure data was carried out to obtain the frequency range of diesel knock. Meanwhile, image segmentation and a tracking algorithm based on YCbCr color space were implemented to determine the frequency range of diesel knock from the obtained high-speed image. The results show that the frequency of diesel knock was dominated by the range from 13 kHz to 15 kHz. Still, frequency with low power existed down until 7 kHz. The frequencies of the area movement were shown to be 13 kHz and, in some cases, 8.67 kHz.
Journal Article

Design and Modeling of a Novel Internal Combustion Engine with Direct Hydraulic Power Take-off

2013-04-08
2013-01-1733
This paper introduces a Hydraulic Linear Engine (HLE) concept and describes a model to simulate instantaneous engine behavior. The United States Environmental Protection Agency has developed an HLE prototype as an evolution of their previous six-cylinder, four-stroke, free-piston engine (FPE) hardware. The HLE design extracts work hydraulically, in a fashion identical to the initial FPE, and is intended for use in a series hydraulic hybrid vehicle. Unlike the FPE, however, the HLE utilizes a crank for improved timing control and increased robustness. Preliminary experimental results show significant speed fluctuations and cylinder imbalance that require careful controls design. This paper also introduces a model of the HLE that exhibits similar behavior, making it an indispensible tool for controls design. Further, the model's behavior is evaluated over a range of operating conditions currently unobtainable by the experimental setup.
Journal Article

Strategy for Mode Transition between Low Temperature Combustion and Conventional Combustion in a Diesel Engine

2013-09-08
2013-24-0058
Mode transition between low temperature combustion (LTC) and conventional combustion was performed by changing the exhaust gas recirculation (EGR) rate from 60% to 0% or vice versa in a light duty diesel engine. The indicated mean effective pressure (IMEP) before mode transition was set at 0.45 MPa, representing the maximum load of LTC in this research engine. Various engine operating parameters (rate of EGR change, EGR path length, and residual gas) were considered in order to investigate their influence on the combustion mode transition. The characteristics of combustion mode transition were analyzed based on the in-cylinder pressure and hydrocarbon (HC) emission of each cycle. The general results showed that drastic changes of power output, combustion noise, and HC emission occurred during the combustion mode transition due to the improper injection conditions for each combustion mode.
Technical Paper

Spray and Combustion Visualization of Gasoline and Diesel under Different Ambient Conditions in a Constant Volume Chamber

2013-10-14
2013-01-2547
Spray and combustion of gasoline and diesel were visualized under different ambient conditions in terms of pressure, temperature and density in a constant volume chamber. Three different ambient conditions were selected to simulate the three combustion regimes of homogeneous charge compression ignition, premixed charge compression ignition and conventional combustion. Ambient density was varied from 3.74 to 23.39 kg/m3. Ambient temperature at the spray injection were controlled to the range from 474 to 925 K. Intake oxygen concentration was also modulated from 15 % to 21 % in order to investigate the effects of intake oxygen concentrations on combustion characteristics. The injection pressure of gasoline and diesel were modulated from 50 to 150 MPa to analyze the effect of injection pressure on the spray development and combustion characteristics. Liquid penetration length and vapor penetration length were measured based on the methods of Mie-scattering and Schileren, respectively.
Technical Paper

Assessment of Soot Particles in an Exhaust Gas for Low Temperature Diesel Combustion with High EGR in a Heavy Duty Compression Ignition Engine

2013-10-14
2013-01-2572
The characteristics of soot particles in an exhaust gas for low temperature diesel combustion (LTC) compared with conventional combustion in a compression ignition engine were experimentally investigated by the elemental and thermogravimetric analysis (TGA). Morphology of soot particles was also studied by the transmission electron microscopy (TEM). From the result of the TGA, the water can be evaporated until about 150°C for both combustion regimes. The soot particles for LTC contained more volatile hydrocarbons, which can be easily evaporated from 200°C to 420°C compared with conventional diesel combustion. The soot oxidation for conventional combustion occurs up to 600°C, on the other hand the particles for LTC is oxidized below 520°C. Elemental analysis showed higher oxygen weight fraction resulted from the oxygenated hydrocarbon for the soot particles in LTC. TEM has shown primary particles to be in a diameter range of 20 to 50 nm for conventional diesel combustion.
Technical Paper

Turbulence Intensity Calculation from Cylinder Pressure Data in a High Degree of Freedom Spark-Ignition Engine

2010-04-12
2010-01-0175
The number of control actuators available on spark-ignition engines is rapidly increasing to meet demand for improved fuel economy and reduced exhaust emissions. The added complexity greatly complicates control strategy development because there can be a wide range of potential actuator settings at each engine operating condition, and map-based actuator calibration becomes challenging as the number of control degrees of freedom expand significantly. Many engine actuators, such as variable valve actuation and flow control valves, directly influence in-cylinder combustion through changes in gas exchange, mixture preparation, and charge motion. The addition of these types of actuators makes it difficult to predict the influences of individual actuator positioning on in-cylinder combustion without substantial experimental complexity.
Technical Paper

The Effect of LPG Composition on Combustion and Performance in a DME-LPG Dual-fuel HCCI Engine

2010-04-12
2010-01-0336
The effect of the composition of propane (C₃H₈) and butane (C₄H₁₀) in liquefied petroleum gas (LPG) was investigated in a dual-fuel HCCI engine fueled with di-methyl ether (DME) and LPG. The composition of LPG affects DME-LPG dual fuel HCCI combustion due to the difference in the physical properties of propane that and butane such as octane number, auto-ignition temperature and heat of vaporization. DME was injected directly into the cylinder at various injection timing from 160 to 350 crank angle degrees (CAD). LPG was injected at the intake port with a fixed injection timing at 20 CAD. It was found that power output was increased with propane ratio. This gain in power output resulted from increased expansion work due to the better anti-knock properties of propane. However, higher propane ratio made combustion efficiency decrease because of the suppression in low temperature reaction of DME which determines heat release amount of high temperature reaction.
Technical Paper

Turbocharger Matching for a 4-Cylinder Gasoline HCCI Engine Using a 1D Engine Simulation

2010-10-25
2010-01-2143
Naturally aspirated HCCI operation is typically limited to medium load operation (∼ 5 bar net IMEP) by excessive pressure rise rate. Boosting can provide the means to extend the HCCI range to higher loads. Recently, it has been shown that HCCI can achieve loads of up to 16.3 bar of gross IMEP by boosting the intake pressure to more than 3 bar, using externally driven compressors. However, investigating HCCI performance over the entire speed-load range with real turbocharger systems still remains an open topic for research. A 1 - D simulation of a 4 - cylinder 2.0 liter engine model operated in HCCI mode was used to match it with off-the-shelf turbocharger systems. The engine and turbocharger system was simulated to identify maximum load limits over a range of engine speeds. Low exhaust enthalpy due to the low temperatures that are characteristic of HCCI combustion caused increased back-pressure and high pumping losses and demanded the use of a small and more efficient turbocharger.
Journal Article

Spray and Combustion Characteristics of Ethanol Blended Gasoline in a Spray Guided DISI Engine under Lean Stratified Operation

2010-10-25
2010-01-2152
An experimental study was performed to evaluate the effects of ethanol blending on to gasoline spray and combustion characteristics in a spray-guided direct-injection spark-ignition engine under lean stratified operation. The spray characteristics, including local homogeneity and phase distribution, were investigated by the planar laser-induced fluorescence and the planar Mie scattering method in a constant volume chamber. Therefore, the single cylinder engine was operated with pure gasoline, 85 %vol, 50 %vol and 25vol % ethanol blended with gasoline (E85, E50, E25) to investigate the combustion and exhaust emission characteristics. Ethanol was identified to have the potential of generating a more appropriate spray for internal combustion due to a higher vapor pressure at high temperature conditions. The planar laser-induced fluorescence image demonstrated that ethanol spray has a faster diffusion velocity and an enhanced local homogeneity.
Journal Article

Comparison of Different Boosting Strategies for Homogeneous Charge Compression Ignition Engines - A Modeling Study

2010-04-12
2010-01-0571
Boosted Homogeneous Charge Compression Ignition (HCCI) has been modeled and has demonstrated the potential to extend the engine's upper load limit. A commercially available engine simulation software (GT-PowerÖ) coupled to the University of Michigan HCCI combustion and heat transfer correlations was used to model a 4-cylinder boosted HCCI engine with three different boosting configurations: turbocharging, supercharging and series turbocharging. The scope of this study is to identify the best boosting approach in order to extend the HCCI engine's operating range. The results of this study are consistent with the literature: Boosting helps increase the HCCI upper load limit, but matching of turbochargers is a problem. In addition, the low exhaust gas enthalpy resulting from HCCI combustion leads to high pressures in the exhaust manifold increasing pumping work. The series turbocharging strategy appears to provide the largest load range extension.
Technical Paper

Influence of EGR and Pilot Injection on PCCI Combustion in a Single-Cylinder Diesel Engine

2011-08-30
2011-01-1823
The effect of pilot injection and exhaust gas recirculation (EGR) on premixed charge compression ignition (PCCI) combustion was investigated in a single-cylinder direct-injection diesel engine with low engine speed and low load. The injection timing of PCCI combustion was fixed at 25 ~ 30 crank angle degree before top dead center (°CA BTDC) based on the ignition delay and power output. The level of oxides of nitrogen (NOx) emissions of PCCI combustion was 68% lower than that of conventional diesel combustion owing to the reduction of near-stoichiometric region which is well known as the main source of NOx formation. However, the indicated mean effective pressure (IMEP), hydrocarbon (HC), particulate matter (PM) and carbon monoxide (CO) emissions deteriorated compared with conventional diesel combustion because of early injection, advanced combustion phase and lowered combustion temperature. EGR has been applied to PCCI combustion.
Technical Paper

Effects of EGR and DME Injection Strategy in Hydrogen-DME Compression Ignition Engine

2011-08-30
2011-01-1790
The compression ignition combustion fuelled with hydrogen and dimethyl-ether was investigated. Exhaust gas recirculation was applied to reduce noise and nitrogen oxide (NOx) emission. When dimethyl-ether was injected earlier, combustion showed two-stage ignitions known as low temperature reaction and high temperature reaction. With advanced dimethyl-ether injection, combustion temperature and in-cylinder pressure rise were lowered which resulted in high carbon monoxide and hydrocarbon emissions. However, NOx emission was decreased due to relatively low combustion temperature. The engine combustion showed only high temperature reaction when dimethyl-ether was injected near top dead center. When exhaust gas recirculation gas was added, the in-cylinder pressure and heat release rate were decreased. However, it retarded combustion phase resulting in higher indicated mean effective pressure.
Technical Paper

Effect of the Multiple Injection on Stratified Combustion Characteristics in a Spray-Guided DISI Engine

2011-09-11
2011-24-0059
In this study, the single-cylinder engine experiment was carried out to investigate the effect of multiple injections on stratified combustion characteristics in a spray-guided direct injection spark ignition engine. The engine was operated at 1200 rpm. The total injection quantity applied was 11 mg/stroke to represent a low-load condition. Single injection and multiple injection were tested. Split ratio of each multiple strategies were 1:1 for double injection and 1:1:1 for the triple injection respectively. Dwell time between each injection was set to 200 μs. In the result of engine experiment with the single injection, indicated mean effective pressure was increased as injection timing was retarded to top dead center due to the increased effective work. However, the retardation of the injection timing was limited by the misfire occurrence resulted from the locally rich mixture generation under the high ambient pressure.
Journal Article

Review of Soot Deposition and Removal Mechanisms in EGR Coolers

2010-04-12
2010-01-1211
Exhaust gas recirculation (EGR) coolers are commonly used in diesel engines to reduce the temperature of recirculated exhaust gases in order to reduce NOX emissions. Engine coolant is used to cool EGR coolers. The presence of a cold surface in the cooler causes fouling due to particulate soot deposition, condensation of hydrocarbon, water and acid. Fouling experience results in cooler effectiveness loss and pressure drop. In this study, possible soot deposition mechanisms are discussed and their orders of magnitude are compared. Also, probable removal mechanisms of soot particles are studied by calculating the forces acting on a single particle attached to the wall or deposited layer. Our analysis shows that thermophoresis in the dominant mechanism for soot deposition in EGR coolers and high surface temperature and high kinetic energy of soot particles at the gas-deposit interface can be the critical factor in particles removal.
Technical Paper

Operating Characteristics of DME-Gasoline Dual-fuel in a Compression Ignition Engine at the Low Load Condition

2013-03-25
2013-01-0049
Combustion and emission characteristics were investigated in a compression ignition engine with dual-fuel strategy using dimethyl ether (DME) and gasoline. Experiments were performed at the low load condition corresponding to indicated mean effective pressure of 0.45 MPa. DME was directly injected into the cylinder and gasoline was injected into the intake manifold during the intake stroke. The proportion of DME in the total input energy was adjusted from 10% to 100%. DME DME injection timing was widely varied to investigate the effect of injection timing on the combustion phase. Injection pressure of DME was varied from 20 MPa to 60 MPa. Exhaust gas recirculation (EGR) was controlled from 0% to 60% to explore the effect of EGR on the combustion and emission characteristics. As DME proportion was decreased with the increased portion of gasoline, the combustion efficiency was decreased but thermal efficiency was increased.
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