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Boosted HCCI Combustion Using Low-Octane Gasoline with Fully Premixed and Partially Stratified Charges

High-load HCCI combustion has recently been demonstrated with conventional gasoline using intake pressure boosting. The key is to control the high combustion heat release rates (HRR) by using combustion timing retard and mixture stratification. However, at naturally aspirated and moderately boosted conditions, these techniques did not work well due to the low autoignition reactivity of conventional gasoline at these conditions. This work studies a low-octane distillate fuel with similar volatility to gasoline, termed Hydrobate, for its potential in HCCI engine combustion at naturally aspirated and low-range boosted conditions. The HCCI combustion with fully premixed and partially stratified charges was examined at intake pressures (Pin) from 100 to 180 kPa and constant intake temperature (60�C) and engine speed (1200 rpm).
Technical Paper

Development of Laser Radar Cruise Control System

The adaptive cruise control (ACC) system reduces the workload of the driver. Lower cost and more precise control are the keys to successfully creating a market with the ACC system. A system that eliminates unexpected acceleration or deceleration caused by incorrect judgment is in high demand. From 1997, the laser radar ACC system has been produced for the domestic version of the Lexus LS400. It provides high recognition capability with a two-dimensional scanning system at an affordable price. Th millimeter wave radar ACC system can perform with better recognition capability, but is quite expensive. While many companies are developing millimeter wave radar ACC systems, we think our laser radar ACC system is superior.
Technical Paper

Ignition Simulation and Visualization for Spark Plug Electrode Design

An ignition simulation and an ignition visualization method that analyze effects of spark plug electrode design have been developed. In the ignition simulation, a programmed heat source corresponds to the discharge energy in the spark gap, and the flame-kernel generation and flame propagation are calculated on the heat balance in the gap, in consideration of thermal transmission to the electrodes. The results by this simulation indicate that high ignitability of fine ground electrode spark plugs is because the miniaturization of the ground electrode reduces the heat loss, and flame growth is thus less disturbed by the loss. The ignition visualization includes taking Schlieren images by laser light to capture flame kernels with weaker luminescence intensity compared to ignition discharge spark luminescence. This visualization enables the observation of the influence of the shape of spark plug electrodes on flame growth.
Technical Paper

Investigation of the Relationship Between DI Diesel Combustion Processes and Engine-Out Soot Using an Oxygenated Fuel

The relationship between combustion processes and engine-out soot was investigated in an optically accessible DI diesel engine using diethylene glycol diethyl ether (DGE) fuel, a viable diesel oxygenate. The high oxygen content of DGE enables operation without soot emissions at higher loads than with a hydrocarbon fuel. The high cetane number of DGE enables operation at charge-gas temperatures below those required for current diesel fuels, which may be advantageous for reducing NOx emissions. In-cylinder optical measurements of flame lift-off length and natural luminosity were obtained simultaneously with engine-out soot measurements while varying charge-gas density and temperature. The local mixture stoichiometry at the lift-off length was characterized by a parameter called the oxygen ratio that was estimated from the measured flame lift-off length using an entrainment correlation for non-reacting sprays.
Technical Paper

Non-Sooting, Low Flame Temperature Mixing-Controlled DI Diesel Combustion

Methods of producing non-sooting, low flame temperature diesel combustion were investigated in an optically-accessible, quiescent constant-volume combustion vessel. Combustion and soot formation processes of single, isolated fuel jets were studied after autoignition and transient premixed combustion and while the injector needle was fully open (i.e., during the quasi-steady mixing-controlled phase of heat-release for diesel combustion).The investigation showed that fuel jets that do not undergo soot formation in any region of the reacting jet and that also have a low flame temperature could be produced in at least three different ways during mixing-controlled combustion: First, using a #2 diesel fuel and an injector tip with a 50 micron orifice, a fuel jet was non-sooting in ambient oxygen concentrations as low as 10% (simulating the use of EGR) for typical diesel ambient temperatures (1000 K) and densities.
Technical Paper

Modeling Iso-octane HCCI Using CFD with Multi-Zone Detailed Chemistry; Comparison to Detailed Speciation Data Over a Range of Lean Equivalence Ratios

Multi-zone CFD simulations with detailed kinetics were used to model iso-octane HCCI experiments performed on a single-cylinder research engine. The modeling goals were to validate the method (multi-zone combustion modeling) and the reaction mechanism (LLNL 857 species iso-octane) by comparing model results to detailed exhaust speciation data, which was obtained with gas chromatography. The model is compared to experiments run at 1200 RPM and 1.35 bar boost pressure over an equivalence ratio range from 0.08 to 0.28. Fuel was introduced far upstream to ensure fuel and air homogeneity prior to entering the 13.8:1 compression ratio, shallow-bowl combustion chamber of this 4-stroke engine. The CFD grid incorporated a very detailed representation of the crevices, including the top-land ring crevice and head-gasket crevice. The ring crevice is resolved all the way into the ring pocket volume. The detailed grid was required to capture regions where emission species are formed and retained.
Technical Paper

Transient Rate of Injection Effects on Spray Development

Transients in the rate of injection (ROI) with respect to time are ever-present in direct-injection engines, even with common-rail fueling. The shape of the injection ramp-up and ramp-down affects spray penetration and mixing, particularly with multiple-injection schedules currently in practice. Ultimately, the accuracy of CFD model predictions used to optimize the combustion process depends upon the accuracy of the ROI utilized as fuel input boundary conditions. But experimental difficulties in the measurement of ROI, as well as real-world affects that change the ROI from the bench to the engine, add uncertainty that may be mistaken for weaknesses in spray modeling instead of errors in boundary conditions. In this work we use detailed, time-resolved measurements of penetration at the Spray A conditions of the Engine Combustion Network to rigorously guide the necessary ROI shape required to match penetration in jet models that allow variable rate of injection.
Technical Paper

Full Cycle CFD Simulations to Study Thermal and Chemical Effects of Fuel Injection during Negative Valve Overlap in an Automotive Research Engine

Recently experiments were conducted on an automotive homogeneous-charge-compression-ignition (HCCI) research engine with a negative-valve-overlap (NVO) cam. In the study two sets of experiments were run. One set injected a small quantity of fuel (HPLC-grade iso-octane) during NVO in varying amounts and timings followed by a larger injection during the intake stroke. The other set of experiments was similar, but did not include an NVO injection. By comparing both sets of results researchers were able to investigate the use of NVO fuel injection to control main combustion phasing under light-load conditions. For this paper a subset of these experiments are modeled with the computational-fluid-dynamics (CFD) code KIVA3V [ 6 ] using a multi-zone combustion model. The computational domain includes the combustion chamber, and intake and exhaust valves, ports, and runners. Multiple cycles are run to minimize the influence of initial conditions on final simulated results.
Journal Article

Application of a Tunable-Diode-Laser Absorption Diagnostic for CO Measurements in an Automotive HCCI Engine

An infrared laser absorption technique has been developed to measure in-cylinder concentrations of CO in an optical, automotive HCCI engine. The diagnostic employs a distributed-feedback, tunable diode laser selected to emit light at the R15 line of the first overtone of CO near 2.3 μm. The collimated laser beam makes multiple passes through the cylinder to increase its path length and its sampling volume. High-frequency modulation of the laser output (wavelength modulation spectroscopy) further enhances the signal-to-noise ratio and detection limits of CO. The diagnostic has been tested in the motored and fired engine, exhibiting better than 200-ppm sensitivity for 50-cycle ensemble-average values of CO concentration with 1-ms time resolution. Fired results demonstrate the ability of the diagnostic to quantify CO production during negative valve overlap (NVO) for a range of fueling conditions.
Journal Article

Boosted HCCI for High Power without Engine Knock and with Ultra-Low NOx Emissions - using Conventional Gasoline

The potential of boosted HCCI for achieving high loads has been investigated for intake pressures (Piⁿ) from 100 kPa (naturally aspirated) to 325 kPa absolute. Experiments were conducted in a single-cylinder HCCI research engine (0.98 liters) equipped with a compression-ratio 14 piston at 1200 rpm. The intake charge was fully premixed well upstream of the intake, and the fuel was a research-grade (R+M)/2 = 87-octane gasoline with a composition typical of commercial gasolines. Beginning with Piⁿ = 100 kPa, the intake pressure was systematically increased in steps of 20 - 40 kPa, and for each Piⁿ, the fueling was incrementally increased up to the knock/stability limit, beyond which slight changes in combustion conditions can lead to strong knocking or misfire. A combination of reduced intake temperature and cooled EGR was used to compensate for the pressure-induced enhancement of autoignition and to provide sufficient combustion-phasing retard to control knock.
Journal Article

An Investigation into the Effects of Fuel Properties and Engine Load on UHC and CO Emissions from a Light-Duty Optical Diesel Engine Operating in a Partially Premixed Combustion Regime

The behavior of the engine-out UHC and CO emissions from a light-duty diesel optical engine operating at two PPCI conditions was investigated for fifteen different fuels, including diesel fuels, biofuel blends, n-heptane-iso-octane mixtures, and n-cetane-HMN mixtures. The two highly dilute (9-10% O₂) early direct injection PPCI conditions included a low speed (1500 RPM) and load (3.0 bar IMEP) case~where the UHC and CO have been found to stem from overly-lean fuel-air mixtures~and a condition with a relatively higher speed (2000 RPM) and load (6.0 bar IMEP)~where globally richer mixtures may lead to different sources of UHC and CO. The main objectives of this work were to explore the general behavior of the UHC and CO emissions from early-injection PPCI combustion and to gain an understanding of how fuel properties and engine load affect the engine-out emissions.
Technical Paper

Stochastic Knock Detection Model for Spark Ignited Engines

This paper presents the development of a Stochastic Knock Detection (SKD) method for combustion knock detection in a spark-ignition engine using a model based design approach. The SKD set consists of a Knock Signal Simulator (KSS) as the plant model for the engine and a Knock Detection Module (KDM). The KSS as the plant model for the engine generates cycle-to-cycle accelerometer knock intensities following a stochastic approach with intensities that are generated using a Monte Carlo method from a lognormal distribution whose parameters have been predetermined from engine tests and dependent upon spark-timing, engine speed and load. The lognormal distribution has been shown to be a good approximation to the distribution of measured knock intensities over a range of engine conditions and spark-timings for multiple engines in previous studies.
Journal Article

Characteristics of Isopentanol as a Fuel for HCCI Engines

Long chain alcohols possess major advantages over the currently used ethanol as bio-components for gasoline, including higher energy content, better engine compatibility, and less water solubility. The rapid developments in biofuel technology have made it possible to produce C 4 -C 5 alcohols cost effectively. These higher alcohols could significantly expand the biofuel content and potentially substitute ethanol in future gasoline mixtures. This study characterizes some fundamental properties of a C 5 alcohol, isopentanol, as a fuel for HCCI engines. Wide ranges of engine speed, intake temperature, intake pressure, and equivalence ratio are investigated. Results are presented in comparison with gasoline or ethanol data previously reported. For a given combustion phasing, isopentanol requires lower intake temperatures than gasoline or ethanol at all tested speeds, indicating a higher HCCI reactivity.
Journal Article

Optical Investigation of UHC and CO Sources from Biodiesel Blends in a Light-Duty Diesel Engine Operating in a Partially Premixed Combustion Regime

The influence of soy- and palm-based biofuels on the in-cylinder sources of unburned hydrocarbons (UHC) and carbon monoxide (CO) was investigated in an optically accessible research engine operating in a partially premixed, low-temperature combustion regime. The biofuels were blended with an emissions certification grade diesel fuel and the soy-based biofuel was also tested neat. Cylinder pressure and emissions of UHC, CO, soot, and NOx were obtained to characterize global fuel effects on combustion and emissions. Planar laser-induced fluorescence was used to capture the spatial distribution of fuel and partial oxidation products within the clearance and bowl volumes of the combustion chamber. In addition, late-cycle (30° and 50° aTDC) semi-quantitative CO distributions were measured above the piston within the clearance volume using a deep-UV LIF technique.
Journal Article

Liquid Penetration of Diesel and Biodiesel Sprays at Late-Cycle Post-Injection Conditions

The liquid and vapor-phase spray penetrations of #2 diesel and neat (100%) soybean-derived biodiesel have been studied at late expansion-cycle conditions in a constant-volume optical chamber. In modern diesel engines, late-cycle staged injections may be used to assist in the operation of exhaust stream aftertreatment devices. These late-cycle injections occur well after top-dead-center (TDC), when post-combustion temperatures are relatively high and densities are low. The behavior of diesel sprays under these conditions has not been well-established in the literature. In the current work, high-speed Mie-scatter and schlieren imaging are employed in an optically accessible chamber to characterize the transient and quasi-steady liquid penetration behavior of diesel sprays under conditions relevant for late-cycle post injections, with very low densities (1.2 - 3 kg/m 3 ) and moderately high temperatures (800 - 1400 K).
Journal Article

Effect of Post Injections on In-Cylinder and Exhaust Soot for Low-Temperature Combustion in a Heavy-Duty Diesel Engine

Multiple fuel-injections during a single engine cycle can reduce combustion noise and improve pollutant emissions tradeoffs. Various hypotheses have been proposed in the literature regarding the in-cylinder processes responsible for the pollutant emissions improvements. This paper provides a brief overview of these hypotheses along with an investigation exploring which of these mechanisms are important for post injections under low-temperature combustion (LTC) conditions in a heavy-duty diesel engine. In-cylinder soot and exhaust smoke are measured by 2-color soot thermometry and filter paper blackening, respectively. The evolution and interaction of soot regions from each of the injections is visualized using high-speed imaging of soot luminosity, both in the piston bowl and in the squish regions.
Journal Article

Influence of the In-Cylinder Flow Field (Tumble) on the Fuel Distribution in a DI Hydrogen Engine Using a Single-Hole Injector

This paper examines the interaction of bulk flow and jet-induced fuel convection in an optically accessible hydrogen-fueled engine with direct injection. Planar laser-induced fluorescence (PLIF) of gaseous acetone as a fuel tracer was performed to obtain quantitative images of the hydrogen mole-fraction in the operating engine. With the engine motored, fuel was injected into inert bulk gas from a centrally located injector during the compression stroke. The injector had a single-hole nozzle with the jet angled at 50 degrees with respect to the vertical injector axis. Two parameters were varied in the experiments, injector orientation and tumble intensity, and for each of these, the injection timing was varied. Image series of the mean fuel mole-fraction between injection and near-TDC crank angles capture the mixture-formation process for each configuration and injection timing.
Journal Article

High Resolution Scalar Dissipation and Turbulence Length Scale Measurements in an Internal Combustion Engine

High resolution planar laser-induced fluorescence (PLIF) measurements were performed in an optically accessible internal combustion (IC) engine to investigate the behavior of scalar dissipation and the fine-scale structures of the turbulent scalar field. The fluorescent tracer fluorobenzene was doped into one of the two intake streams and nitrogen was used as the carrier gas to permit high signal-to-noise ratio fluorescence measurements without oxygen quenching effects. The resulting two-dimensional images allowed for an analysis of the structural detail of the scalar and scalar dissipation fields defined by the mixing of the two adjacent intake streams. High levels of scalar dissipation were found to be located within convoluted, sheet-like structures in accordance with previous studies. The fluorescence data, which were acquired during the intake stroke, were also used to examine the scalar energy and dissipation spectra.
Journal Article

Thermal and Chemical Effects of NVO Fuel Injection on HCCI Combustion

Fuel injection during negative valve overlap (NVO) can extend low-load gasoline HCCI operation through control of main combustion phasing. Reactions and heat release accompanying NVO fuel injection give rise to changes in temperature and composition of the charge prior to main combustion. The extent of reaction of injected NVO fuel and the relative importance of resulting thermal and chemical effects on main combustion are a current research topic. In this work, bulk temperature computations are used to quantify thermal conditions prior to main ignition for cases with and without NVO fueling. To separate measured thermal effects from chemical effects of NVO fuel reactions on the main combustion, cases without NVO fuel but with similar mixture temperatures and combustion phasing are compared. Effects of varying NVO fuel amount and injection timing on heat release, combustion phasing, bulk temperature evolution, and iso-octane ignition temperatures are analyzed.