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Technical Paper

“Wetting” the Appetite of Spark Ignition Engines for Lean Combustion

Single-cylinder spark ignition engine experiments conducted at constant speed, fixed airflow, and using isooctane as the fuel, demonstrated the effects of fuel-air mixture preparation on lean operation. Mixture preparation was changed by varying the time of fuel injection in the induction manifold, near the intake valve port. For comparison, a prevaporized fuel-air mixture was also investigated. Emphasis was placed on determining the effects of mixture preparation on combustion characteristics. Based on the results from this study, the often favored prevaporized mixture of fuel and air may not be the best diet for lean engine operation.
Technical Paper

“Prediction of In-Cylinder Pressure, Temperature, and Loads Related to the Crank Slider Mechanism of I.C. Engines: A Computational Model”

This paper describes the initial works related to the study of Internal Combustion Engines, as an object of mechanical design, at the Universidad Tecnológica de Pereira. It is reported a concise, complete methodology for simple model of internal combustion engine. The emphasis of the paper is placed on the use of the in-cylinder parameters (pressure and temperature) and inertial loads in the crank-slider mechanism to derive the loads that act on all the components of the crank-slider mechanism as well as the theoretical output torque for a given geometrical structure and inertial properties. These loads can then be used to estimate the preliminary dimensions of engine components in the initial stage of engine development. To obtain the pressure and temperature inside the cylinder, under different operation parameters, such as air fuel ratio and spark angle advance, a Zero dimensional model is applied. The heat transfer from the cylinder and friction are not taken into account.
Technical Paper

“OptiVent” - A New Approach for Controlling Mass Air Flow and Combustion in Direct Injection SI-Engines

Combustion concepts for future SI engines try to meet CO2-emission commitments and legislation all over the world. Where the Diesel engine has an advantage by principle, the efficiency of the SI engine has to be improved significantly, while of course the exhaust emissions must not become worse. An approach is to reduce the gas exchange losses using fully variable valve trains on the intake side of the combustion engine. OptiVent is a patented new way of controlling the mass air flow in the cylinder of a combustion engine using opening valves during the compression phase of a four stroke engine. This technology regards a wider range of variability on the valvetrain components of the engine especially for opening the valves more than one time during a cycle. On the other hand it is necessary to combine this technology with direct injection to avoid fuel losses in the exhaust system and raising the exhaust hydrocarbon emission of the engine.
Technical Paper

“Doing More with Less” - The Fuel Economy Benefits of Cooled EGR on a Direct Injected Spark Ignited Boosted Engine

Due to the rising costs of fuel and increasingly stringent regulations, auto makers are in need of technology to enable more fuel-efficient powertrain technologies to be introduced to the marketplace. Such powertrains must not sacrifice performance, safety or driver comfort. Today's engine and powertrain manufacturers must, therefore, do more with less by achieving acceptable vehicle performance while reducing fuel consumption. One effective method to achieve this is the extreme downsizing of current direct injection spark ignited (DISI) engines through the use of high levels of boosting and cooled exhaust gas recirculation (EGR). Key challenges to highly downsized gasoline engines are retarded combustion to prevent engine knocking and the necessity to operate at air/fuel ratios that are significantly richer than the stoichiometric ratio.
Technical Paper

λDSF: Dynamic Skip Fire with Homogeneous Lean Burn for Improved Fuel Consumption, Emissions and Drivability

Dynamic skip fire (DSF) has shown significant fuel economy improvement potential via reduction of pumping losses that generally affect throttled spark-ignition (SI) engines. In DSF operation, individual cylinders are fired on-demand near peak efficiency to satisfy driver torque demand. For vehicles with a downsized-boosted 4-cylinder engine, DSF can reduce fuel consumption by 8% in the WLTC (Class 3) drive cycle. The relatively low cost of cylinder deactivation hardware further improves the production value of DSF. Lean burn strategies in gasoline engines have also demonstrated significant fuel efficiency gains resulting from reduced pumping losses and improved thermodynamic characteristics, such as higher specific heat ratio and lower heat losses. Fuel-air mixture stratification is generally required to achieve stable combustion at low loads.
Technical Paper

α-Pinene - A High Energy Density Biofuel for SI Engine Applications

This study proposes a novel biofuel for spark ignition (SI) engine, α-pinene (C10H16), which is non-oxygenated and thus has a gravimetric energy density comparable to that of hydrocarbon fuels. The ignition characteristics of α-pinene were evaluated in an ignition quality tester (IQT) under standard temperature and pressure conditions. The measured ignition delay time (IDT) of α-pinene is 10.5 ms, which is lower than that of iso-octane, 17.9 ms. The estimated research octane number (RON) for pinene from IQT is 85. A temperature sweep in IQT showed that that α-pinene is less reactive at low temperatures, but more reactive at high temperatures when compared to isooctane. These results suggest that α-pinene has high octane sensitivity (OS) and is suitable for operation in turbocharged SI engines. With these considerations, α-pinene was operated in a single cylinder SI engine.
Technical Paper

Wideband SI Engine Lambda Control

Long term control of the AFR (Air/Fuel Ratio) of spark ignition engines is currently accomplished with a selvoscillating PI control loop. Because of the intake/exhaust time delay, the oscillation frequency and hence bandwidth of this loop is small. This paper describes a new approach to the design of this control loop using a novel observer system. In this way the bandwidth of this important loop is increased by a factor of 2 - 6 times, leading to more accurate overall AFR control. Moreover the observer approach is so robust and allows such feedback levels that it reduces significantly the accuracy required in the calibration of the base fuel control system with which it is be used. It can be used with either conventional- or advanced observer based- base fuel strategies.
Technical Paper

Why Intake Charge Dilution Decreases Nitric Oxide Emission from Spark Ignition Engines

This study was undertaken to develop a better understanding of how intake charge dilution by various gases affected nitric oxide (NO) emission from a single-cylinder spark ignition engine. Carbon dioxide, nitrogen, helium, argon, steam, and exhaust gas were individually added to the intake charge of a propane-fueled, single-cylinder engine operated at constant speed and load. Nitric oxide emission was reduced in all cases. The gases with higher specific heats gave larger NO reductions. The product of diluent flow rate and specific heat correlated with NO reduction. The effects of diluents on calculated combustion temperature, mbt spark timing, and fuel consumption are also presented and discussed.
Technical Paper

Where Closed Rankine Cycles Fit - with Examples of Automotive APS and Portable GPS

Rankine powerplant advantages are found to fit best applications that call for long maintenance free life, or where the heat energy is essentially free as in bottoming and topping cycles, or in special environments as undersea or space. Worthy applications suggested on the basis of potential market size and ability to satisfy customer imposed cost and performance are: automotive and tank accessory power systems (APS), transportable refrigeration, portable power supply (GPS), standby power, remote site power, and home air conditioner drive. The automotive APS and a 1 1/2 kWe GPS are further analyzed. The APS can offer attractive features to the automobile user, including the possibility of reducing pollution from spark ignition engine. The GPS is an example showing high cost effectiveness for long operating times. It is recommended that marketing and cost studies continue, and that working fluid and heat exchanger technologies be accentuated.
Technical Paper

What Limits Lean Operation in Spark Ignition Engines-Flame Initiation or Propagation?

The lack of clearly identified constraints for ignition and flame propagation has hindered understanding the processes which limit lean operation in spark ignition engines. This experimental study explores flame initiation and flame propagation as limits of lean operation in engines. In separate tests conducted in a single-cylinder CFR (cooperative fuel research) engine, the spark timing was either advanced or retarded from MBT* in order to determine the ignition-limit or partial-burn-limit spark timings, respectively. These two limiting spark timings were found to converge at lean mixtures. At the MBT lean misfire limit, the ignition-limit, and the partial-burn-limit spark timing lines converged. Apparently flame initiation as well as flame propagation considerations constrain lean operation. The effects of engine and ignition system-related variables on the ignition and partial-burn limits are presented and discussed.
Technical Paper

Wear Studies on an Automotive Gasoline Engine Using Methanol Gasoline Blends - A Study of the Effects of Variables

This paper presents wear results of the top piston ring for an automotive spark ignited engine using gasoline and methanol blends. The Radiotracer Technique was employed utilising the multichannel analyser. In order to assess the wear process resulting due to each single factor viz. fuel type, engine speed, bhp and the water jacket temperature, investigations were carried out based on a series of statistically designed experiments. The design matrix employed a one half replication of 24 set. The study showed that the speed and load of an engine markedly affect the top ring wear. Use of alcohol blended fuels was found to marginally increase wear especially at low operating temperatures.
Technical Paper

Wavelet Analysis of In-Cylinder LDV Measurements and Correlation Against Heat-Release

Wavelet analysis was used to calculate turbulence and mean velocity levels for LDV measurements made in a four valve spark ignition engine. Five different camshafts were tested, and they produce significantly different flow behaviour. The standard cam gives tumble and with valve deactivation, swirl is produced. One camshaft with early inlet valve closing and two camshafts with late inlet valve closing were also tested. The wavelet toolbox for Matlab version 5.1 has been used for the wavelet calculations. The wavelet technique produces both time resolved and frequency resolved velocity information. The results indicate some influence of the turbulence frequency content on the rate of heat release. Correlation against heat-release can be seen for different scales of turbulence. The breakdown of the tumble (low frequency turbulence) into high frequency turbulence can be seen clearly.
Technical Paper

Water-Gasoline Fuels-Their Effect on Spark Ignition Engine Emissions and Performance

Single-cylinder engine tests, an analytical engine cycle simulation, and automobile tests were employed to study the effects of supplementing gasoline with water for use in spark ignition engines. Factors examined include: the method of water addition (both water-in-gasoline emulsions and direct manifold water addition), antiknock characteristics with water addition, MBT spark requirement, indicated engine efficiency, engine cooling requirement, exhaust emissions, volumetric efficiency, lean operating limit, smoke level, exhaust temperature, and vehicle driveability. Among the negative aspects of water addition were increased hydrocarbon emissions and decreased vehicle driveability. Also, the polyoxyethylene type of emulsifier used in the water-in-gasoline emulsions, gave poor fuel stability and caused a rapid buildup of engine deposits. However on the positive side, water-gasoline fuels have higher octane ratings and decrease nitric oxide emissions.
Technical Paper

Water Tolerability of Methanol-Gasoline Blends (Phase Separation and SI Engine Performances)

The most important problem arizing from methanol-gasoline is the phase separation caused by the presence of very small quantities of water. Two or three layers showing cloud points were observed after the addition of a small quantity of water, and their separation ratio could not be ascribed to their original blends ratio of methanol and gasoline. The greater the increase methanol content, the greater the increase in the amount of the lower layer and the limit of water absorption. Engine dynamometer tests were conducted on a 0.33L, 4-stroke spark ignition engine to get the effects of supplying the phase separation fuels on engine performances. The results of the separation behavior and the engine dynamometer tests are presented here and discussed.
Journal Article

Water Injection: a Technology to Improve Performance and Emissions of Downsized Turbocharged Spark Ignited Engines

Knock occurrence and fuel enrichment, which is required at high engine speed and load to limit the turbine inlet temperature, are the major obstacles to further increase performance and efficiency of down-sized turbocharged spark ignited engines. A technique that has the potential to overcome these restrictions is based on the injection of a precise amount of water within the mixture charge that can allow to achieve important benefits on knock mitigation, engine efficiency, gaseous and noise emissions. One of the main objectives of this investigation is to demonstrate that water injection (WI) could be a reliable solution to advance the spark timing and make the engine run at leaner mixture ratios with strong benefits on knock tendency and important improvement on fuel efficiency.
Technical Paper

Water Injection to Improve Direct Injection Spark Ignition Engine Efficiency

The increasing use of downsized turbocharged gasoline engines for passengers cars and the new European homologation cycles (WLTC and RDE) both impose an optimization of the whole engine map. More weight is given to mid and high loads, thus enhancing knock and overfueling limitations. At low and moderate engine speeds, knock mitigation is one of the main issues, generally addressed by retarding spark advance thereby penalizing the combustion efficiency. At high engine speeds, knock still occurs but is less problematic. However, in order to comply with thermo-mechanical properties of the turbine, excess fuel is injected to limit the exhaust gas temperature while maximizing engine power, even with cooled exhaust manifolds. This also implies a decrease of the combustion efficiency and an increase in pollutant emissions. Water injection is one way to overcome both limitations.
Journal Article

Water Injection to Enhance Performance and Emissions of a Turbocharged Gasoline Engine under High Load Condition

The potential benefits of water injection on performance and emissions were investigated on a downsized PFI twin-cylinder turbocharged spark ignition engine. Experiments were carried out at high load condition (~15.5 bar IMEP) within the engine speed range from 3500 to 4500rpm with a step of 500 rpm. For each test case the effect of the injected water quantity on combustion and exhaust emissions was investigated by sweeping from 10%w to 30%w the water to gasoline ratio. The water was injected at the same timing as the gasoline by a low pressure injection system external controlled. Tests were performed at WOT conditions exploring, for each operating condition, a spark sweep from knock-free up to knock-limited operation. Compared to the full gasoline reference case, the water injection allowed to advance extensively the spark timing without knock occurrence. The 20% water to gasoline mass fraction gave the best improvements in terms of IMEP.
Technical Paper

Water Injection in IC - SI Engines to Control Detonation and to Reduce Pollutant Emissions

In this paper the effects of water injection in the intake pipe of a single-cylinder standard CFR engine are investigated from an experimental viewpoint. Research was carried out at AGIP Petroli and ISAB ERG Refineries of Priolo Gargallo (SR). Tests were performed according to ASTM Research and Motor Method. Water was supplied by a continuous and pulsed injection system. The engine was fed with low Octane Number (O.N.) base gasoline (cheap products, intermediate of refinery processes). The water to fuel mass flow rate ratio was varied in the range 0 to 2. Measurements of O.N. have shown that water injection virtually increases the water/fuel mixture O.N. and that it is possible to obtain a correct run feeding the engine with a low octane number fuel. The pollutant emissions measurements confirm the effectiveness of water injection in reducing the engine environmental impact.
Journal Article

Water Injection as an Enabler for Increased Efficiency at High-Load in a Direct Injected, Boosted, SI Engine

In a Spark-Ignited engine, there will come a point, as load is increased, where the unburned air-fuel mixture undergoes auto-ignition (knock). The onset of knock represents the upper limit of engine output, and limits the extent of engine downsizing / boosting that can be implemented for a given application. Although effective at mitigating knock, requiring high octane fuel is not an option for most markets. Retarding spark timing can extend the high load limit incrementally, but is still bounded by limits for exhaust gas temperature, and spark retard results in a notable loss of efficiency. Likewise, enriching the air-fuel mixture also decreases efficiency, and has profound negative impacts on engine out emissions. In this current work, a Direct-Injected, Boosted, Spark-Ignited engine with Variable Valve Timing was tested under steady state high load operation. Comparisons were made among three fuels; an 87 AKI, a 91 AKI, and a 110 AKI off-road only race fuel.
Technical Paper

Water Injection Effects In A Single-Cylinder CFR Engine

Though analysed by a few researches, the practice of water injection in Spark Ignition Engines (SI-ICE) does not yield homogeneous results, owing to various typologies of engines used for experiments. In this paper the effects of water injection in the intake pipe are investigated from both a theoretical and experimental viewpoint. Pressure vs. time diagrams were recorded on a single-cylinder CFR engine at AGIP PETROLI, Priolo (CT). Tests were performed according to Research and Motor Method (ASTM). Water was supplied by a continuous injection system inclusive of comparatively high pressure pump. The engine was fed with low O.N. base gasoline (cheap products, intermediate of refinery processes). The water to fuel mass flow rate ratio was varied in the range 0 to 1.5. The NOx emissions measurements confirm the tremendous effectiveness of water injection in reducing the engine environmental impact.