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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.

The model described here is a dynamic mean value model which is small enough to be realized on a microcomputer. Nevertheless it contains significant and very accurate information on the gross internal variables of an engine (the indicated efficiency, scavenge ratio, scavenge efficiency, etc.). This makes the model useful for control and expert system application on line and/or in parallel with an operating diesel engine. Moreover, because of its simplicity, it gives an overall picture of engine operation which is not possible with more complex single engine cycle models. Comparisons with time dependent experimental data show that the model is very accurate both for static and dynamic predictions of engine performance over a large operating range.

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.

In general most engine models for control applications have been constructed using regressions fitting and measured engine data. Such techniques have also been used to model the dynamic performance of engines. Unfortunately regression equation models are very complex and do not show directly the physical reality from which they emerge. This has for example made it impossible to write down explicitly the dymanic equations for, for example, the air exchange process in an SI engine in any form other than as the manifold pressure state equation. In recent a publication a Mean Value Engine Model (MVEM) has been constructed for an SI engine which is physically based and which has a simple physical form which can be immediately understood and manipulated.

Given the rather complicated set of coordinated control inputs which are necessary to control a spark ignition engine, primary control system development and evaluation can be a very difficult task. It is also difficult to develop microprocessor systems which are flexible enough for rapid system reconfiguration. In this paper it is shown that a Personal Computer (PC) provides an excellent solution to this common problem. Possible execution time problems are avoided by the use of a special multitasking environment and simple external hardware. The external hardware takes care of the cycle to cycle fueling and spark advance timing calculations. The PC itself uses its execution time only for calculating new fueling pulse widths and spark advance angles when the operating point of the engine changes. There is also extra computing capacity available for system simulations, condition monitoring, fault detection or perhaps driver information.

One of the most important operating modes for SI engines is in the idle speed region. This is because SI engines spend a large part of their time operating in this mode. Moreover, a large measure of operator satisfaction is dependent on an engine operating smoothly and reliably in and around idle. In particular the operator expects that the idle speed will remain constant in spite of the engine loads due to power steering pumps and air conditioning compressors. In the idle speed region an SI engine is thought to be quite nonlinear because the engine loading can be quite significant, thus forcing the engine to be driven through a reasonably large portion of its lower operating range. Many of the earlier studies of idle speed control systems have dealt with linearized models which in principle have limited validity for the problem at hand. In order to improve this situation, it is necessary to deal with the more general nonlinear control problem.

In earlier work it has been shown that a nearly ideal solution to the problem of accurate estimation of the air mass flow to a central fuel injection (CFI) (or throttle body (TBI)) or EFI (or multi-point (MPI)) equipped engine is provided by using a closed loop nonlinear observer for the engine. With proper design this observer was shown to be both accurate and robust with respect to modelling end measurement errors. It is based on a Constant Gain Extended Kalman Filter (CGEKF). Since the publication of this work, another type of observer has emerged in the literature for which claims of great robustness have been made. This observer is based on new developments in the area of nonlinear control theory and is called a Sliding Mode Observer (SMO). In this paper these two types of observers are compared theoretically and experimentally on an engine mounted on a dynamometer. A very aggressive driving scenario is assumed for these tests.

Many modern control strategies for engine control are based on event based sampling. Operating the control strategy in the event domain makes it possible to obtain samples at specific crank shaft angles in the engine cycle, which is often desirable for certain control strategies. One of the biggest disadvantages involved with event based strategies is signal aliasing at low engine speeds or a high computational burden at higher engine speeds. This paper presents an easy solution to the aliasing problem above. If the data between the event based samples is stored using a time based strategy, it is shown here that a subsequent treatment of the sampled data as a time series together with a suitable low pass filter structure can avoid aliasing.

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.

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.

Many existing production engine controllers use event (or constant crank angle increment) based sampling and computation systems. Because the engine events are synchronized to the internal physical processes of an engine, it is widely accepted that this is the most logical approach to engine control. It is the purpose of this paper to deal with this assumption in detail and to illuminate various failures of it in practical systems. The approach of the paper is in terms of overall general control system design. That is to say that the problem of event based engine control is considered as a general control problem with its standard components: 1. modelling (engine plus actuator/sensor), 2. specification of desired performance goals, 3. control system design method selection and 4. experimental testing.

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.

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.

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.

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.

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.

The effects of lubricant composition on hydrocarbon emissions from a SI engine have been experimentally investigated. Results based on measurements of solubilities of different fuel components in different types of lubricants are presented. 2 lubricants and two hydrocarbons were chosen for testing in a single cylinder engine. Emissions and performance was measured for various fuel air ratios and ignition timings. The lubricant with the lowest solubility with respect to isooctane also showed the lowest hydrocarbon emissions. The influence of the lubricant was greatest at lean air fuel ratios. Xylene is much more soluble in the lubricants than isooctane and gave lower hydrocarbon emissions when the engine was operated at rich air fuel ratios. At leaner mixtures, isooctane gave lower emissions. The results indicate that the lubricant plays a contributing, but not dominating role in hydrocarbon emissions from gasoline engines.

The effects of mixture turbulence on combustion in a spark-ignition engine were investigated using a CFR engine. The apparent instantaneous turbulent flame speed during combustion was calculated from a combustion heat release model that used measured cylinder pressures and assumed spherical flame propagation. This flame speed was correlated with turbulent intensities measured in the motored engine. The ratio of fully developed turbulent flame speed to laminar flame speed was found to be a linear function of motored turbulent intensity.

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 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.