Fuels Characterization for Use in Internal Combustion Engines

It is important provide mathematical functions able to fit with great precision experimental data on gases properties, in order to obtain reliable results when computerized models on IC engines are used. On the basis of experimental data on equilibrium constants (for dissociation phenomena occurring during combustion process in IC engines) new mathematical functions have been determined to fit experimental data. In comparison to traditional fitting polynomials, these new mathematical functions present a great accuracy in matching experimental data. These new mathematical functions have the functional forms of a V order Logarithmic Polynomial, and their coefficients have been evaluated on the basis of the least square method. The new V order Logarithmic Polynomials have been determined for several dissociation reactions according to internal combustion processes applications. V order Logarithmic Polynomials have been implemented also to describe the trend of specific heat at constant pressure Vs temperature and enthalpy Vs temperature. These new Logarithmic Polynomials have been calculated for several gases and fuels for IC engines applications. The new Logarithmic Polynomials pointed out a better precision in comparison to the others polynomial functions used in literature, and the possibility to utilize a single Logarithmic Polynomial for a wide temperature range, according to a good accuracy with experimental data. Another advantage of the Logarithmic Polynomials is the possibility to extrapolate experimental data on a wide temperature range (25% of experimental T range) in order to supply to the experimental data shortage.

A Stochastic Simulation of an HCCI Engine Using an Automatically Reduced Mechanism

Homogeneous Charge Compression Ignition (HCCI) Engines are a promising alternative to the existing Spark Ignition Engines and Compression Ignition Engines. In an HCCI engine, the premixed fuel/air mixture ignites when sufficiently high temperature and pressure is reached. The entire bulk will auto-ignite at almost the same time because the physical conditions are similar throughout the combustion chamber. Therefore it is a justified assumption to consider the chemical reactions to be the rate-determining step for the ignition process. This gives us the opportunity to formulate a simple zero-dimensional model with detailed chemical kinetics for the calculations of the ignition process. Ignition calculations using this model have predicted a high sensitivity to fluctuations in temperature and fuel compositions. These predictions have later been confirmed by experiments. Partially stirred plug flow reactor (PaSPFR) can be used to conquer the assumption of homogeneity. The assumption is replaced by that of statistical homogeneity and thus statistical fluctuations caused by inhomogeneities can be studied. However, the CPU-time needed for this approach is increased considerably and the usage of mechanism reduction becomes evident. In this paper, we demonstrate how a reduced mechanism for natural gas as fuel is derived automatically. The original mechanism by Warnatz (589 reactions, 53 species) is first reduced to a skeletal mechanism (481 reactions, 43 species). By introduction of the quasi steady state assumption, the skeletal mechanism is reduced further to 23 species and 20 global reactions. The accuracy of the final mechanism is demonstrated using the stochastic reactor tool for an HCCI engine.

Development of a Phenomenological Combustion Simulation for a Dual Fuel Engine

A phenomenological cycle simulation for a dual fuel engine has been developed to mathematically simulate the significant processes of the engine cycle, to predict specific performance parameters for the engine, and to investigate approaches to improve performance and reduce emissions. The simulation employs two zones (crevice and unburned) during the processes of exhaust, intake, compression before fuel injection starts, and expansion after combustion ends. From the start of fuel injection to the end of combustion, several, zones are utilized to account for crevice flow, diesel fuel spray, air entrainment, diesel fuel droplet evaporation, ignition delay, flame propagation, and combustion quenching. The crevice zone absorbs charge gas from the cylinder as pressure increases, and releases mass back into the chamber as pressure decreases. Some crevice mass released during late combustion may not be oxidized, resulting in emissions of hydrocarbon and carbon monoxide. Quenching ahead of the flame front may leave additional charge unburned, yielding high methane emissions. Potential reduction of engine-out NOx emissions with natural gas fueling has also been investigated. The higher substitution of natural gas in the engine produces less engine-out NOx emissions. This paper presents the development of the model, baseline predictions, and comparisons to experimental measurements performed in a single-cylinder Caterpillar 3400 series engine.

A Multiple-Zone Cycle Simulation for Spark-Ignition Engines: Thermodynamic Details

A thermodynamic cycle simulation was developed for a spark-ignition engine which included the use of multiple zones for the combustion process. This simulation was used to complete analyses for a commercial, spark-ignition V-8 engine operating at a part load condition. Specifically, the engine possessed a compression ratio of 8.1:1, and had a bore and stroke of 101.6 and 88.4 mm, respectively. A part load operating condition at 1400 rpm with an equivalence ratio of 1.0 was examined. Results were obtained for overall engine performance, for detailed in-cylinder events, and for the thermodynamics of the individual processes. In particular, the characteristics of the engine operation with respect to the combustion process were examined. Implications of the multiple zones formulation for the combustion process are described.

High Efficiency and Low NOx Gas Engines for Co-Generation Markets

Lean-burn gas engines are operating worldwide because of having an advantage of lower NOx emission and higher thermal efficiency than those of stoichiometric gas engines. The modern lean-burn gas engines, especially medium and large size, have the pre-combustion chamber technology. On the contrary, there are some problems that originate in the spark plug. Particularly near the ignition plug located in the center, the fuel gas density is lean, affected by the lean-gas mixture coming from the main combustion chamber during the compression stroke and the fuel gas density near the wall is rich. The lifetime of ignition plug is likely to be shorter than those used in the conventional theoretical mixture gas combustion engine, because the required voltage for the plug is high, which reaches 20–25 kV or more. The authors and their colleagues have studied a combustion method of using micro-pilot fuel oil instead of spark plug as an ignition source in recent four years to provide a solution for the above mentioned technical problems. The energy of micro-pilot fuel oil is equivalent to 1% of the total thermal input, but the energy of the pilot fuel oil is several thousands times of the spark ignition. According to the author’s study, NOx emission level is defined by the amount of pilot fuel oil. But only about 1% fuel can meet the NOx target. NOx emission level meets TA-Luft of 500 mg/m3N @ 5% O2. Even the regulation of 200 ppm @ 0% O2 in the Japanese large cities can be achieved, this level is almost corresponding to the half TA-Luft. This paper describes the performance being desired for gas engines through the service-experience in co-generation fields and also describes the newly developed gas engine corresponding to a 1000 kW class, which has micro-pilot fuel oil ignition method. This engine has the same performance of a diesel engine, BMEP of 2.3 MPa and brake thermal efficiency of 43%.

Dual-Fuel System for Heavy Duty Truck Engines

Increasing emphasis on natural gas as a clean, economical and abundant fuel advocates its increasing use in transportation applications. In developing countries like Pakistan and India where, more than 80% of the goods are transported by trucks and where natural gas is available in abundance, development of natural gas conversion systems for heavy-duty truck engines offers a viable option to replace the use of expensive imported fuels. A complete dual-fuel (natural gas/diesel) conversion system developed using mostly commercially available components, for the Hino EC-100 diesel engine is described. Both diesel and natural gas operating modes are possible, without undermining normal engine performance as a diesel. The conversion system has performance similar to the ‘straight diesel’ operation, with comparable efficiency at full load. Furthermore, particulate and oxide of nitrogen (NOx) emissions are considerably lower than on diesel, however, carbon monoxide and hydrocarbon exhaust emissions are higher, particularly at light load.

Characteristics of Premixed Combustion Type Diesel Engine Using Hollow Cone Spray

To realize the pre-mixed combustion type Diesel engine, analyses of the wide-angle conical spray flow and its application to the direct injection Diesel engine have been made. In the present work, the spray was evaluated by high speed flow visualization, particle image velocimetry (PTV) measurement, phase Doppler anemometer (PDA) measurement and numerical simulation by KTVA-3V code, and finally the combustion and exhaust characteristics of the proposed engine are examined. The penetration and the shape of the conical sprays under different ambient pressures (0.1, 1.0 and 2.0 MPa) are obtained experimentally and with numerical simulations. Generally, good agreements between them are achieved. It is also cleared that the spray formation is strongly influenced by the surrounding pressure. PIV measurements show the initial development of the spray. The maximum velocity is about 80 m/s, which is almost in the same range as that obtained by the PDA measurements. For the combustion experiment, the excess air ratio was set at 3.1 and 2.5. The engine speed was varied from 1000 to 2000 rpm. Expected premixed combustion region is realized at around the fuel injection timing prior to 65 degree BTDC, where NOx and soot emissions are almost zero at the excess air ratio of 3.1.

Hydrogen Peroxide Effect on HCCI Performance

Methane fueled Homogeneous Charged Compression Ignition (HCCI) combustion is investigated using detailed kinetic modeling. Control of heat release rate is identified as the biggest challenge against HCCI operation. A new control strategy, hydrogen peroxide (H2O2) addition, along with intake mixture preheating, is proposed to resolve this problem. A single-zone perfectly stirred reactor type formulation is employed with detailed chemical kinetic mechanism to predict homogeneous gas-phase chemical kinetics. The effects of H2O2 addition on the performance parameters of a methane-fueled HCCI engine are simulated. The results show that HCCI performance can be improved radically by the addition of H2O2 since it lowers the ignition delay time substantially. The resulting NOx concentration in high IMEP operating conditions is significantly less than that emitted from conventional internal combustion engines. Possibility of increasing NOx emissions with increasing initial temperature has been shown. Reduction in carbon monoxide emission is predicted with the addition of H2O2 via the increased hydroxyl chemistry. More flexible control of HCCI operation is possible by regulating the amount of H2O2 added.

Passenger-Car Fuel Consumption Versus Performance in Retrospect

Over the last quarter of the 1900s, the U.S. Environmental Protection Agency (EPA) has annually tabulated the fuel economy and performance characteristics of the new passenger-car fleet. Fuel economy was measured over the EPA combined urban and highway driving schedules. The performance metric was the estimated acceleration time from a standing start to 60 miles per hour (mph). In the present study, the interplay among factors influencing these characteristics is reviewed. Then, for the average new car in a given year, the manner in which fuel consumption and acceleration time are influenced by vehicle weight and engine power are examined. The departure of individual vehicles from this average trend is considered. Finally, a few of the prominent powertrain characteristics responsible for improvements in the tradeoff between fuel consumption and performance are listed.

Combustion Characteristics of Spark Ignition Engine Fuelled by LPG

Experimental studies have been carried out for investigating engine performance parameters, cylinder pressure, emissions and engine thermal balance of spark ignition engine (S.I.E.) using either gasoline or Liquefied Petroleum Gases (LPG) as a fuel at maximum brake torque (MBT) ignition timing. MBT ignition timing for LPG is found to be 2 to 10 degrees crank angle more advance than for gasoline. Maximum cylinder pressure locations for gasoline and LPG are shifted towards top dead center (TDC) with increase engine speed. At low engine speed, maximum cylinder pressure for gasoline fuel is higher than for LPG fuel. At high engine speeds maximum cylinder pressure for LPG is nearly the same as for gasoline. Maximum pressure for ignition timing 35 crank angle (CA) before top dead center (BTDC) is greater than for 45 and 25 CA respectively. Engine produces more brake power with gasoline than with LPG. Engine brake thermal efficiency (ηbth) and volumetric efficiency (ηv) with LPG is less than for gasoline. When S.I.E converted from gasoline to LPG the loss in maximum power is nearly 14% and the loss in maximum efficiency is nearly 8%. UHC and CO concentrations for LPG are nearly one-tenth of that produced by gasoline at the same ignition timing and the same engine speed. For low engine speed exhaust and oil temperatures for gasoline and LPG increase with increase engine speed but for high engine speed exhaust and oil temperature decreases with increase engine speed. For gasoline and LPG cooling water temperature decreases with increase engine speed. Lubricating oil and cooling water temperatures for gasoline and LPG increase with increase ignition timing BTDC but exhaust gas temperature decreases with increase ignition timing. LPG has higher exhausted gas temperature than gasoline but gasoline has higher oil temperature than LPG. At different ignition timing exhaust loss for LPG is greater than for gasoline but cooling water loss for gasoline is greater than for LPG.