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Technical Paper

Auto-Oil Program Phase II Heavy Hydrocarbon Study: Analysis of Engine-Out Hydrocarbon Emissions Data

1994-10-01
941966
The engine-out (EO) total and speciated hydrocarbon emissions data from the Auto-Oil Program Phase II Heavy Hydrocarbon Study had been analyzed. The methodology was to first investigate the stabilized EO emissions (Bag 2) of a specific vehicle (Vehicle 04B, a 1989 Model Year Ford Taurus); then the vehicle-to-vehicle differences in Bag2 emissions were considered. Finally, the differences in the Bag2 and the starting/warm-up EO emissions (Bag1) were examined. The speciated emissions may be interpreted as a “feed-through” part due to the unreacted fuel species, and an “offset” part due to the decomposition products. The significant non-fuel emitted species were methane and the olefins. The HC emissions for vehicles with different total emissions were similar in species composition. For both the total and speciated emissions, there was no substantial difference between the Bag1 and Bag2 values for Vehicle 04B.
Technical Paper

Novel Experiment on In-Cylinder Desorption of Fuel from the Oil Layer

1994-10-01
941963
A technique has been developed to measure the desorption and subsequent oxidation of fuel in the oil layer by spiking the oil with liquid fuel and firing the engine on gaseous fuel or motoring with air. Experiments suggest that fuel desorption is not diffusion limited above 50 °C and indicated that approximately two to four percent of the cylinder oil layer is fresh oil from the sump. The increase in hydrocarbon emissions is of the order of 100 ppmC1 per 1% liquid fuel introduced into the fresh oil in a methane fired engine at mid-speed and light load conditions. Calculations indicate that fuel desorbing from oil is much more likely to produce hydrocarbon emissions than fuel emerging from crevices.
Technical Paper

Experimental Investigation of Smoke Emission Dependent upon Engine Operating Conditions

1997-05-01
971658
Smoke is emitted in diesel engines because fuel injected into the combustion chamber burns with insufficient oxygen. The emission smoke from diesel engines is a very important air pollution problem. Smoke emission, which is believed to be largely related to the diffusion combustion in diesel engines, results from pyrolysis of fuel not mixed with air. Therefore, the smoke emission is dependent on diffusion combustion phenomena, which are controlled by engine parameters. This paper presents an analysis of combustion by relating the smoke emission with heat release in diesel engines. An analysis is made of the diffusion combustion quantity, the smoke emission, and the fraction of diffusion combustion as related to the engine parameters which are air-fuel ratio, injection timing, and engine speed.
Technical Paper

Effects of Piston-Ring Dynamics on Ring/Groove Wear and Oil Consumption in a Diesel Engine

1997-02-24
970835
The wear patterns of the rings and grooves of a diesel engine were analyzed by using a ring dynamics/gas flow model and a ring-pack oil film thickness model. The analysis focused primarily on the contact pressure distribution on the ring sides and grooves as well as on the contact location on the ring running surfaces. Analysis was performed for both new and worn ring/groove profiles. Calculated results are consistent with the measured wear patterns. The effects of groove tilt and static twist on the development of wear patterns on the ring sides, grooves, and ring running surfaces were studied. Ring flutter was observed from the calculation and its effect on oil transport was discussed. Up-scraping of the top ring was studied by considering ring dynamic twist and piston tilt. This work shows that the models used have potential for providing practical guidance to optimizing the ring pack and ring grooves to control wear and reduce oil consumption.
Technical Paper

A Piston Ring-Pack Film Thickness and Friction Model for Multigrade Oils and Rough Surfaces

1996-10-01
962032
A complete one-dimensional mixed lubrication model has been developed to predict oil film thickness and friction of the piston ring-pack. An average flow model and a roughness contact model are used to consider the effects of surface roughness on both hydrodynamic and boundary lubrication. Effects of shear-thinning and liner temperature on lubricant viscosity are included. An inlet condition is applied by considering the unsteady wetting location at the leading edge of the ring. A ‘film non-separation’ exit condition is proposed to replace Reynolds exit condition when the oil squeezing becomes dominant. Three lubrication modes are considered in the model, namely, pure hydrodynamic, mixed, and pure boundary lubrication. All of these considerations are crucial for studying the oil transport, asperity contact, and friction especially in the top dead center (TDC) region where the oil control ring cannot reach.
Technical Paper

Chemical Kinetic Modeling of the Oxidation of Unburned Hydrocarbons

1992-10-01
922235
The chemistry of unburned hydrocarbon oxidation in SI engine exhaust was modeled as a function of temperature and concentration of unburned gas for lean and rich mixtures. Detailed chemical kinetic mechanisms were used to model isothermal reactions of unburned fuel/air mixture in an environment of burned gases at atmospheric pressure. Simulations were performed using five pure fuels (methane, ethane, propane, n-butane and toluene) for which chemical kinetic mechanisms and steady state hydrocarbon (HC) emissions data were available. A correlation is seen between reaction rates and HC emissions for different fuels. Calculated relative amounts of intermediate oxidation products are shown to be consistent with experimental measurements.
Technical Paper

The Possible Role of Surface Tension in the Reduction of Top Ring Drag

1993-10-01
932781
In a small (4.5 KW) diesel engine, Laser Induced Fluorescence (LIF) has been used to produce detailed oil film thickness measurements around the top piston ring and liner near midstroke. The flow is “Newtonian” under the ring in the sense that using a high shear rate viscosity at the liner temperature is appropriate. The geometry corresponds everywhere to that required for a valid Reynolds approximation. Classical boundary conditions are not applicable for the high strain rates (106-107 s-1) under the piston rings of typical modem engines. A new boundary condition is developed to explain the data. The exit surface shear stress is shown to scale with a Marangoni-like (surface tension gradient) effect. By increasing surface tension, it is possible to make substantial reductions in friction for a fixed high shear viscosity.
Technical Paper

Autoignition of Alcohols and Ethers in a Rapid Compression Machine

1993-10-01
932755
The autoignition characteristics of methanol, ethanol and MTBE (methyl tert-butyl ether) have been investigated in a rapid compression machine at pressures in the range 20-40 atm and temperatures within 750-1000 K. All three oxygenated fuels tested show higher autoignition temperatures than paraffins, a trend consistent with the high octane number of these fuels. The autoignition delay time for methanol was slightly lower than predicted values using reported reaction mechanisms. However, the experimental and measured values for the activation energy are in very good agreement around 44 kcal/mol. The measured activation energy for ethanol autoignition is in good agreement with previous shock tube results (31 kcal/mol), although ignition times predicted by the shock tube correlation are a factor of three lower than the measured values. The measured activation energy for MTBE, 41.4 kcal/mol, was significantly higher than the value previously observed in shock tubes (28.1 kcal/mol).
Technical Paper

Flame Kernel Development in a Methanol Fueled Engine

1993-10-01
932649
The combustion behavior in a modem 4-valve engine using a broad range of methanol/gasoline fuel mixtures was studied. The initial flame development was examined by using a spark plug fiber optics probe. Approximately, the kernel expansion speed, Sg, is relatively unchanged from M0 to M40; jumps by ∼30% from M40 to M60; and then remains roughly constant from M60 to M100. Statistics of the IMEP indicate that at a lean idle condition the combustion rate and robustness correlate with Sg: a higher value of Sg gives better combustion. Thus M60-M100 fuels give better idle combustion behavior than the M0-M40 fuels.
Technical Paper

Photographic and Performance Studies of Diesel Combustion With a Rapid Compression Machine

1974-02-01
740948
Photographic and performance studies with a Rapid Compression Machine at the Massachusetts Institute of Technology have been used to develop insight into the role of mixing in diesel engine combustion. Combustion photographs and performance data were analyzed. The experiments simulate a single fuel spray in an open chamber diesel engine with direct injection. The effects of droplet formation and evaporation on mixing are examined. It is concluded that mixing is controlled by the rate of entrainment of air by the fuel spray rather than the dynamics of single droplets. Experimental data on the geometry of a jet in a quiescent combustion chamber were compared with a two-phase jet model; a jet model based on empirical turbulent entrainment coefficients was developed to predict the motion of a fuel jet in a combustion chamber with swirl. Good agreement between theory and experiment was obtained.
Technical Paper

Dual-Fuel Gasoline-Alcohol Engines for Heavy Duty Trucks: Lower Emissions, Flexible-Fuel Alternative to Diesel Engines

2018-04-03
2018-01-0888
Long-haul and other heavy-duty trucks, presently almost entirely powered by diesel fuel, face challenges meeting worldwide needs for greatly reducing nitrogen oxide (NOx) emissions. Dual-fuel gasoline-alcohol engines could potentially provide a means to cost-effectively meet this need at large scale in the relatively near term. They could also provide reductions in greenhouse gas emissions. These spark ignition (SI) flexible fuel engines can provide operation over a wide fuel range from mainly gasoline use to 100% alcohol use. The alcohol can be ethanol or methanol. Use of stoichiometric operation and a three-way catalytic converter can reduce NOx by around 90% relative to emissions from diesel engines with state of the art exhaust treatment.
Technical Paper

Real World Performance of an Onboard Gasoline/Ethanol Separation System to Enable Knock Suppression Using an Octane-On-Demand Fuel System

2018-04-03
2018-01-0879
Higher compression ratio and turbocharging, with engine downsizing can enable significant gains in fuel economy but require engine operating conditions that cause engine knock under high load. Engine knock can be avoided by supplying higher-octane fuel under such high load conditions. This study builds on previous MIT papers investigating Octane-On-Demand (OOD) to enable a higher efficiency, higher-boost higher compression-ratio engine. The high-octane fuel for OOD can be obtained through On-Board-Separation (OBS) of alcohol blended gasoline. Fuel from the primary fuel tank filled with commercially available gasoline that contains 10% by volume ethanol (E10) is separated by an organic membrane pervaporation process that produces a 30 to 90% ethanol fuel blend for use when high octane is needed. In addition to previous work, this paper combines modeling of the OBS system with passenger car and medium-duty truck fuel consumption and octane requirements for various driving cycles.
Technical Paper

More Efficient Combustion in Small Open Chamber Diesel Engines

1972-02-01
720775
Until quite recently, it appeared that there was an effective lower limit on bore size in open-chamber diesel engines. This paper presents a technique for improving combustion in the small open-chamber diesel engine. Recent work at MIT on a 2-1/2 in bore, short-stroke diesel engine has demonstrated that good efficiency can be obtained through a combination of a large-hole nozzle and the use of air swirl to prevent overpenetration. There is some indication that good efficiency can be obtained over a wider operating range than standard diesel practice. A method of design analysis for this type of engine is presented, along with techniques for estimating the swirl and nozzle design parameters.
Technical Paper

Alcohol Fueled Heavy Duty Vehicles Using Clean, High Efficiency Engines

2010-10-25
2010-01-2199
Non-petroleum based liquid fuels are essential for reducing oil dependence and greenhouse gas generation. Increased substitution of alcohol fuel for petroleum based fuels could be achieved by 1) use in high efficiency spark ignition engines that are employed for heavy duty as well as light duty operation and 2) use of methanol as well as ethanol. Methanol is the liquid fuel that is most efficiently produced from thermo-chemical gasification of coal, natural gas, waste or biomass. Ethanol can also be produced by this process but at lower efficiency and higher cost. Coal derived methanol is in limited initial use as a transportation fuel in China. Methanol could potentially be produced from natural gas at an economically competitive fuel costs, and with essentially the same greenhouse gas impact as gasoline. Waste derived methanol could also be an affordable low carbon fuel.
Technical Paper

Using Mass Spectrometry to Detect Ethanol and Acetaldehyde Emissions from a Direct Injection Spark Ignition Engine Operating on Ethanol/Gasoline Blends

2011-04-12
2011-01-1159
Ethanol and acetaldehyde emissions from a direct ignition spark ignition were measured using mass spectrometry. Previous methods focused on eliminating or minimizing interference from exhaust species with identical atomic mass and fragment ions created in ionization process. This paper describes a new technique which exploits the fragment ions from ethanol and acetaldehyde. A survey of mass spectra of all major species of exhaust gas was conducted. It was found that ethanol contributes most ions in mass number 31 and that no other gas species produces ions at this mass number. Acetaldehyde detection suffers more interference. Nevertheless, it was estimated that detection at mass number 43 is possible with 10% error from 2-methylbutane. This new technique was validated in an engine experiment. By running the engine with pure gasoline and E85, the validity of the technique can be checked.
Technical Paper

Oil Conditioning as a Means to Minimize Lubricant Ash Requirements and Extend Oil Drain Interval

2009-06-15
2009-01-1782
A novel approach to condition the lubricant at a fixed station in the oil circuit is explored as a potential means to reduce additive requirements or increase oil drain interval. This study examines the performance of an innovative oil filter which releases no additives into the lubricant, yet enhances the acid control function typically performed by detergent and dispersant additives. The filter chemically conditions the crankcase oil during engine operation by sequestering acidic compounds derived from engine combustion and lubricant degradation. Long duration tests with a heavy-duty diesel engine show that the oil conditioning with the strong base filter reduces lubricant acidity (TAN), improves Total Base Number (TBN) retention, and slows the rate of viscosity increase and oxidation. The results also indicate that there may be a reduction in wear and corrosion.
Technical Paper

A New Approach to Ethanol Utilization: High Efficiency and Low NOx in an Engine Operating on Simulated Reformed Ethanol

2008-10-06
2008-01-2415
The use of hydrogen as a fuel supplement for lean-burn engines at higher compression ratios has been studied extensively in recent years, with good promise of performance and efficiency gains. With the advances in reformer technology, the use of a gaseous fuel stock, comprising of substantially higher fractions of hydrogen and other flammable reformate species, could provide additional improvements. This paper presents the performance and emission characteristics of a gas mixture of equal volumes of hydrogen, CO, and methane. It has recently been reported that this gas mixture can be produced by reforming of ethanol at comparatively low temperature, around 300C. Experiments were performed on a 1.8-liter passenger-car Nissan engine modified for single-cylinder operation. Special pistons were made so that compression ratios ranging from CR= 9.5 to 17 could be used. The lean limit was extended beyond twice stoichiometric (up to lambda=2.2).
Technical Paper

Fuel Effects on HCCI Operation in a Spark Assisted Direct Injection Gasoline Engine

2011-08-30
2011-01-1763
The fuel effects on HCCI operation in a spark assisted direct injection gasoline engine are assessed. The low load limit has been extended with a pilot fuel injection during the negative valve overlap (NVO) period. The fuel matrix consists of hydrocarbon fuels and various ethanol blends and a butanol blend, plus fuels with added ignition improvers. The hydrocarbon fuels and the butanol blend do not significantly alter the high or the low limits of operation. The HCCI operation appears to be controlled more by the thermal environment than by the fuel properties. For E85, the engine behavior depends on the extent that the heat release from the pilot injected fuel in the NVO period compensates for the evaporative cooling of the fuel.
Technical Paper

Optimizing Base Oil Viscosity Temperature Dependence For Power Cylinder Friction Reduction

2014-04-01
2014-01-1658
Lubricant viscosity along the engine cylinder liner varies by an order of magnitude due to local temperature variation and vaporization effects. Tremendous potential exists for fuel economy improvement by optimizing local viscosity variations for specific operating conditions. Methods for analytical estimation of friction and wear in the power-cylinder system are reviewed and used to quantify opportunities for improving mechanical efficiency and fuel economy through lubricant formulation tailored specifically to liner temperature distributions. Temperature dependent variations in kinematic viscosity, density, shear thinning, and lubricant composition are investigated. Models incorporating the modified Reynolds equation were used to estimate friction and wear under the top ring and piston skirt of a typical 11.0 liter diesel engine.
Technical Paper

A Model For Estimating Oil Vaporization From The Cylinder Liner As A Contributing Mechanism to Engine Oil Consumption

1999-05-03
1999-01-1520
A model has been developed for estimating the oil vaporization rate from the cylinder liner of a reciprocating engine. The model uses input from an external cycle simulator and an external liner oil film thickness model. It allows for the change in oil composition and the change in oil film thickness due to vaporization. It also estimates how the passage of the compression and scraper rings combine with the vaporization to influence the steady-state composition of the oil layer in the upper ring pack. Computer model results are presented for a compression-ignition engine using a range of liner temperatures, several engine speeds, and two different oils. Vaporization is found to be highly dependent on liner temperature and steady-state oil composition. The steady-state oil composition near the top of the cylinder is found to be significantly different than the composition of the oil near the bottom of the cylinder.
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