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The paper describes the optimization of a 50 cc crankcase scavenged two-stroke diesel engine operating on dimethyl ether (DME). The optimization is primarily done with respect to engine efficiency. The underlying idea behind the work is that the low weight, low internal friction and low engine-out NOx of such an engine could make it ideal for future vehicles operating on second-generation biofuels. Data is presented for the performance and emissions at the current state of development of the engine. Brake efficiencies above 30% were obtained despite the small size of the engine. In addition, efficiencies near the maximum were found over a wide operating range of speeds and loads. Maximum bmep is 500 kPa. Results are shown for engine speeds ranging from 2000 to 5000 rpm and loads from idle to full load. At all speeds and loads NOx emissions are below 200 ppm and smokeless operation is achieved. Design improvements relative to an earlier prototype are described.

The low auto-ignition temperature, rapid evaporation and high cetane number of dimethyl ether (DME) enables the use of low-pressure direct injection in compression ignition engines, thus potentially bringing the cost of the injection system down. This in turn holds the promise of bringing CI efficiency to even the smallest engines. A 50cc crankcase scavenged two-stroke CI engine was built based on moped parts. The major alterations were a new cylinder head and a 100 bar DI system using a GDI-type injector. Power is limited by carbon monoxide emission but smoke-free operation and NOx < 200ppm is achieved at all points of operation.

With the current trend towards engine downsizing, the use of turbochargers to obtain extra engine power has become common. A great difficulty in the use of turbochargers is in the modelling of the compressor map. In general this is done by inserting the compressor map directly into the engine ECU (Engine Control Unit) as a table. This method uses a great deal of memory space and often requires on-line interpolation and thus a large amount of CPU time. In this paper a more compact, accurate and rapid method of dealing with the compressor modelling problem is presented. This method is physically based and is applicable to all turbochargers with radial compressors for either Spark Ignition (SI) or diesel engines.

The issues addressed in this paper are investigation of the wear mechanisms present in the standard lubricity test for diesel oil: The High frequency Reciprocating Rig (HFRR). The HFRR is a laboratory wear test using a ball on disk configuration. The result of a test is the wear scar diameter (WSD) on the ball. Up to now, all analyses indicated that fuel viscosity influences the wear scar size and fuel performance in full-scale pumps. The wear scar size could then be a result of hydrodynamic lubrication (at least a significant part of it) and not of boundary lubrication as it was the original intention of the test. The appearance of an excellent volatile fuel for diesel engines, Dimethyl Ether (DME), has resulted in new wear tests such as the Medium Frequency Pressurised Reciprocating Rig (MFPRR), a pressurised version of the HFRR. DME has a about 25 times lower viscosity than diesel oil so the MFPRR viscosity sensibility issue is seriously aggravated for this fuel.

This paper describes the development and test of a viscometer capable of handling dimethyl Ether (DME) and other volatile fuels. DME has excellent combustion characteristics in diesel engines but the injection equipment can break down prematurely due to extensive wear when handling this fuel. It was established, in earlier work, that the wear in the pumps is substantial even if the lubricity of DME is raised to a believed acceptable level using anti-wear additives. An influence of the viscosity on the wear in the pumps was suspected. The problem, up to now, was that the viscosity of DME has only been estimated or calculated but never actually measured. In the present work a volatile fuel viscometer (VFVM) was developed. It is of the capillary type and it was designed to handle DME, neat or additised. The kinematic and dynamic viscosities of pure DME were measured at 0.185 cSt and 0.122 cP at 25 °C respectively.

This paper describes the development and test of a method capable of determining the lubricity of low boiling point fuels with emphasis on Dimethyl Ether (DME). DME has excellent combustion characteristics but diesel engine injection equipment can break down due to extensive wear when handling this fuel. Earlier work has established that the lubricity of neat DME is considerably lower than that of diesel oil and kerosene. The repeatability of the results in this former work was poor though. In the present work, the Medium Frequency Pressurised Reciprocating Rig 2 (MFPRR2) was developed and tested. In this apparatus the influence of the frictional force on the load magnitude was eliminated resulting in a drastic improvement of the repeatability. The lubricity of DME was attempted redressed by adding either commercial wear reducing agents or a high lubricity fuel. A very few ppm of additive raised the lubricity of DME considerably to a level above the one of kerosene.

Mean Value Engine Models (MVEMs) are simplified, dynamic engine models which are physically based. Such models are useful for control studies, for engine control system analysis and for model based engine control systems. Very few published MVEMs have included the effects of Exhaust Gas Recirculation (EGR). The purpose of this paper is to present a modified MVEM which includes EGR in a physical way. It has been tested using newly developed, very fast manifold pressure, manifold temperature, port and EGR mass flow sensors. Reasonable agreement has been obtained on an experiemental engine, mounted on a dynamometer.

An important paradigm for the modelling of naturally aspirated (NA) spark ignition (SI) engines for control purposes is the Mean Value Engine Model (MVEM). Such models have a time resolution which is just sufficient to capture the main details of the dynamic performance of NA SI engines but not the cycle-by-cycle behavior. In principle such models are also physically based, are very compact in a mathematical sense but nevertheless can have reasonable prediction accuracy. Presently no MVEMs have been constructed for intercooled turbocharged SI engines because their complexity confounds the simple physical understanding and description of such engines. This paper presents a newly constructed MVEM for a turbocharged SI engine which contains the details of the compressor and turbine characteristics in a compact way. The model has been tested against the responses of an experimental engine and has reasonable accuracy for realistic operating scenarios.

An investigation has been performed of some of the characteristics of di-methyl ether (DME) during high pressure injection in a diesel fuel injection system with a single hole nozzle. Recent developments in the use of DME as an alternate fuel for diesel engines are discussed. The effects of fuel compressibility on compression work are compared for DME and typical hydrocarbon fuel components. Photographs of the transient injection process into room temperature Nitrogen are given for a range of chamber pressures. For a single hole injector, spray penetrations can be predicted using existing correlations for diesel fuel, provided DME fuel properties are used.

Studies were performed with three commonly used additive metals, cerium copper, and iron, with a conventional and a low sulfur fuel in order to investigate fuel additive effects on engine particulate emissions before a particulate filter. Measurements were made on a 4 cylinder direct injection diesel engine and included total particulate mass, soluble organic fraction for both fuels, and polynuclear aromatic hydrocarbon emissions for the low sulfur fuel. The cerium based additive reduced the emissions with both fuels, with the largest effect being on the non-SOF fraction. With the other additives and the high sulfur fuel, non-SOF emissions were increased, increasing total particulate emissions. Copper was found to reduce the polynuclear aromatic hydrocarbons, and cerium was found to have the least effect. The use of an SiC wall flow filter reduced particulate and polynuclear aromatic emissions by over 90%.

Mean Value Engine Models (MVEMs) are dynamic models which describe dynamic engine variable (or state) responses as mean rather than instantaneous values on time scales slightly longer than an engine event. Such engine variables are the independent variables in nonlinear differential (or state) equations which can be quite compact but nevertheless quite accurate. One of the most important of the differential equations for a spark ignition (SI) engine is the intake manifold filling (often manifold pressure) state equation. This equation is commonly used to estimate the air mass flow to an SI engine during fast throttle angle transients to insure proper engine fueling. The purpose of this paper is to derive a modified manifold pressure state equation which is simpler and more physical than those currently found in the literature. This new formulation makes it easier to calibrate a MVEM for different engines and provides new insights into dynamic SI engine operation.

A new method has been developed to close the ends of a wall flow filterused for removing particulate matter from diesel engine exhaust. In thismethod, the ends of the honeycomb structure are capped by deforming andclosing the ends of the channel walls between the extrusion and firingstages of production. The method increases the amount of filtration area per filter volume for agiven cell geometry conpared to the traditional plugging method, since theentire length of the honeycomb channels is used for filtration purposes. In addition, use of the capping method has a beneficial effect on thepressure loss characteristics of a filter with a given filtration area.These benefits are illustrated through experimental results.

The electronic injection and control of gasoline engines has caused a revolution of the conventional four-stroke and two-stroke SI engines. Now, this technique is also playing a more and more important role in the Diesel engine area. In this paper, we will focus on the electronic injection and control of Diesel engines to discuss injection systems, dynamic models and advanced controls. First, the typical R&D results on first generation and second generation of the electronic Diesel injection systems will be reported. Different design approaches will be described. Then, dynamic submodels of the Diesel fuel injection systems and dynamic models for the whole Diesel engine will be summarized. The main dynamic processes and modelling philosophy will be analyzed. Finally, the advanced Diesel governing techniques and Diesel management systems will be reviewed.

Initially, a new direct digital Diesel fuel injection system: an electronic Pump-Pipe-Valve-Injector system was introduced. A general comparison of this system with other electronic Diesel injection systems indicated that the new system can be more effective for high pressure Diesel injection and more flexible for wide engine speed range. Then, the digital injection control characteristics of this system were studied by both experiment and computer simulation. Some special digital injection control functions were obtained. In particular, it was found that transient effect of the control valve action can be used to regulate the pulsed Diesel fuel flow to achieve a low initial injection rate and high injection cut-off rate. This effect can be optimized by appropriate selection of the control valve location. Finally, a direct digital Diesel engine governing technique was investigated.

Due to increasing problems with corrosive wear in marine Diesel Engines, caused by sulphuric acid, it is necessary to understand the mechanism of corrosion. Based on experience with large marine diesel engine operation, a mechanism model is proposed and verified by comparison with practical experience. From operation of engines it is known that the corrosion problem is most severe where the lubrication of the liner is most unsatisfactory. Therefore, most effort is put into modelling the formation and transportation of acid in the lubricant film area. Results from modelling the risk of corrosion during different engine operation conditions are presented.

Many of the materials which have been developed for use as particle filters in the exhaust of diesel engines have characteristics which give rise to significant problems in practical use. Due to its special characteristics, it is shown that SiC is very well suited for use as the base material for particulate filters. The physical and thermal properties of porous SiC substrate material as applied to diesel particulate filters have been determined and are presented. Experimental results from several types of filter regeneration processes in exhaust gas systems confirm the improvements in the area of thermal load and reduction in temperature level during regeneration. The reduction in temperature during regeneration is shown to be consistent with the high thermal conductivity of SiC.

The use of vegetable oil methyl esters has been proposed as an alternative fuel for diesel engines. The purpose of this study is to investigate the combustion of soybean oil methyl ester in a direct injection diesel engine, and compare it to that of a conventional diesel fuel. Experimental measurements of performance, emissions, and rate of heat release were performed as a function of engine load for different fuel injection timings, and injector orifice diameters. It was found that overall, the soybean oil methyl ester behaved comparably to diesel fuel in terms of performance and rate of heat release. The methyl ester fuel gave lower HC emissions and smoke number than diesel fuel at optimum operating conditions. The results for CO emissions were varied. NOx emissions were strongly related to the cylinder pressure development. Changing the injection orifice diameter had less effect on engine performance when using diesel fuel, than with methyl ester fuel.

Conventional electronic engine control systems suffer from poor transient air/fuel ratio control accuracy. This is true of speed-throttle, speed-density, and mass air flow (MAF) control systems with either single point (or central) or port fuel injection. The reason for this is that they fail to 1. compensate for the nonlinear dynamics of the fuel film in the intake manifold or in the vicinity of the intake valves. 2. estimate correctly the air mass flow at the location of the injector(s). This paper presents a nonlinear fuel film compensation network and a nonlinear closed loop observer. The nonlinear fuel film compensator gives improved global cancellation of the fuel film dynamics, while the closed loop observer has improved robustness with respect to modelling error and measurement noise. The closed loop observer is based on a modified constant gain extended Kalman filter.

Many existing classical electronic control systems (speed-throttle, speed-density, MAF (mass air flow)) are based on quasistatic engine models and static measured engine maps. They are thus time consuming to adapt to new engine types, are sensitive to dynamic sensor errors and in general have undesirable dynamic characteristics. One of the main reasons for the characteristics of these strategies has been the lack of a precise, systems oriented, equation based, dynamic engine model. Recently a compact dynamic mean value engine model (MVEM) has been presented by the authors which displays good global accuracy. A mean value model is one which predicts the mean value of the gross internal and external engine variables. This paper shows how the engine model can be applied to the systematic design and analysis of classical electronic engine control systems. One of the main aims of the paper is to eliminate the use of cut and try methods in designing dynamic engine controls.

A model which calculates the hydrocarbon emissions from an SI engine is presented. The model was developed in order to obtain a better under-standing of experimental results from an engine operating on different fuels and lubricants. The model is based on the assumptions that fuel is stored in crevices and oil film during intake and compression followed by desorption during expansion and exhaust. The model also calculates the amount of desorbed material that undergoes in cylinder oxidation and exhaust port oxidation. The model succesfully predicts the trends followed by varying different engine parameters. The effect of changing the lubricant is of the same order of magnitude as found experimentally, but the effect of changing the fuel could not be predicted very well by the model. A possible explanation is, that the lubricant film thickness varies due to viscosity variations of the oil film, when the fuel is dissolved in the film.