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Injection rate control is considered as an effective way to optimize diesel combustion process, decrease emission and improve fuel economy. There are many injection rate shaping devices, but most of them still suffer from structure complexity and parameter sensitivity which limit their effectiveness and practicality. A new initial injection rate control method in solenoid-controlled diesel injection systems is introduced in this paper. The basic idea of this method is to maintain a small spill passage between plunger chamber and inlet port during initial injection period. The initial injection rate can be regulated by changing the closing timing of the solenoid-controlled spill valve. This method has the advantages of simple construction, flexible adjustment and stable performance. Computer aided analysis and design based on a simulation program of the system is conducted to compare and select the sizes of the small spill passage according to their effect on injection characteristics.

This paper describes improvements achieved with regard to the long term stability and the system integrability of a previously described thick film NOx sensor for gasoline lean burn and diesel applications. (1, 2, 3) Durability test up to 1000 hours consisting of a temperature cycle have been carried out by a stoichiometric operating gasoline engine test bench. The NOx sensor demonstrates the NOx output shift in terms of the NOx sensitivity less than 5 % on a model gas apparatus and ± 7 % measuring accuracy in practical operating condition on a diesel engine after 1000 hours that is equivalent to approximately 60K miles driving. The integration of the control electronics for the sensor in its connector is achieved for the sensitive measuring current in the μA-range or less on vehicle applications. The developed electronics functions closed-loop controls for a tip temperature and oxygen pumps as well as a diagnosis of sensor malfunctions.

Gasoline Direct Injection (GDI) is today more regarded as a suitable technology for relatively high displacement engines. The literature shows that the R&D effort on GDI engines is generally made for bores larger than 80 mm. But because GDI appears to be the most relevant way to improve fuel efficiency of S.I. engines, it should also be considered for small bore engines (bore below 75 mm). Nevertheless, locating an injector in already congested cylinder heads, with ultra lean stratified combustion capability while maintaining high engine specific power and proper cylinder head cooling is a real challenge. For such an engine, IFP “narrow spacing” proposal is a 3-valve per cylinder layout or NSDI-3 concept, with a spark-plug-close-to-the-injector design and a suitable piston to confine the fuel spray within the vicinity of the ignition location. This paper describes stage by stage the prototype engine realization using this novel concept.

An overview of work relating to the investigation of direct injection gasoline engines is presented. Comparisons between conventional port-injected and two separate gasoline direct injection combustion systems are drawn. The comparison is between two of the main alternative GDI systems currently under consideration, reverse tumble charge motion with high-pressure swirl-type fuel injector (RTGDI) and low-pressure air-assist direct injection (AAGDI). This comparison was carried out using a 444cc single cylinder research engine of Cosworth Technology design. Included in the discussion are the influence of GDI systems on volumetric efficiency and performance at full load and fuel efficiency and emissions at part load. Techniques to aid the development and calibration of GDI systems are discussed, including Moving Geometry CFD analysis and Design of Experiments (DOE).

The paper presents an analysis of the influence of the most important factors that affect the working process of a direct injection spark ignition engine, especially the injection timing. In the first part of the paper we study the engine's constructive solution and the changes in the engine's performances induced by the alteration of the compression ratio. This phase allowed us to choose the most appropriate variant. In the second part we study the influence of the injection timing over the engine's performances, for two different compression ratios and two injection rates. The most significant results are emphasized using the engine's speed characteristics, determined on the test bed.

The first part of the paper gives an overview of the current development status of the GDI system layout for the middle displacement engine, typically 2 liter, using the stoichiometric or weak lean concept. Hereafter are discussed the particular requirements for the transition to a small displacement/small bore engine working in stratified lean conditions. The paper continues with a description of the application of the different steps of the optimization methodology for a 1.2 liter, small bore 4 cylinder engine from its original base line MPI version towards the lean stratified operation mode. The latest changes in the combustion model, used in the numerical simulation software applied to the combustion chamber design, are discussed and comparison made with the previous model. The redesign of the combustion chamber geometry, the proper choice of injector atomizer type and location and the use of two-stage injection and multi-spark strategies are discussed in detail.

Intake flow simulations were carried out for a prototype DISI engine using the standard k-ε model and the RNG k-ε model. The results were compared with PTV (transient water analog) measurements. The study was focused on low load operations with engine speed at 400 rev/min. Two cases were studied, a single intake case in which one intake port was blocked and a dual intake port case. In the computations, the results show that the standard k-ε model tends to produce higher turbulence levels when turbulence is generated and decays faster when turbulence dissipates. Different turbulence models predict almost the same flow structures. However, the effects of the turbulence model on the predicted tumble and swirl ratios are significant. The TKE distributions at BDC predicted by the two models are also different. The standard k-ε model seems to be more diffusive. Good agreements with PTV data were obtained in the single valve case with the RNG k-ε model.

Fuel preparation and stratified combustion were studied for a conceptual gasoline Direct-Injection Spark-Ignition (GDI or DISI) engine by computer simulations. The primary interest was on the effects of different injector orientations and the effects of tumble ratio for late injection cases at a partial load operating condition. A modified KIVA-3V code that includes improved spray breakup and wall impingement and combustion models was used. A new ignition kernel model, called DPIK, was developed to describe the early flame growth process. The model uses Lagrangian marker particles to describe the flame positions. The computational results reveal that spray wall impingement is important and the fuel distribution is controlled by the spray momentum and the combustion chamber shape. The injector orientation significantly influences the fuel stratification pattern, which results in different combustion characteristics.

Numerical analysis of the flow field and fuel spray in a gasoline direct-injection (GDI) engine is performed by a modified version of the KIVA code. A simple valve treatment technique is employed to handle multiple moving valves without difficulties in generation of a body-fitted grid. The swirl motion of a hollow-cone spray is simulated by injecting droplets with initial angular momentum around the nozzle periphery. The model for spray-wall impingement is based on single droplet experiments with the droplet behaviors after impingement determined by experimental correlations. Different behaviors of an impinging droplet depend on the wall temperature and the critical temperature of fuel with the fuel film taken into account. The test engine is a 4-stroke 4-valve gasoline engine with a pent-roof head and vertical ports to form a reverse tumble flow during the intake stroke. A hollow-cone spray by a high-pressure swirl injector is employed to enhance mixture preparation and mixing.

Numerical simulation was carried out to investigate the effect of transient in-cylinder air motion on fuel spray characteristics in a side-injection gasoline direct injection engine. KIVA-3V code with a fuel spray impingement model was used to simulate a swirl flow driven stratification for a late injection mode. For better understanding of in-cylinder air motion during the induction and compression strokes a flat piston and a bowled piston are compared with each other. Also a simplified simulation considering only the compression stroke was compared with the full simulation. As the high-pressure fuel spray jet flow is much stronger than ambient swirl and tumble flow in the present combustion system the spray development shows similar behavior in both simulations.

Low NOx combustion is possible by PREDIC (PREmixed lean DIesel Combustion) in which fuel is injected at a very early stage of the compression stroke and the combustion starts at near the top dead center by self-ignition. To simplify the phenomenon of the PREDIC process, the test engine was operated with gaseous fuels added to intake air to realize combustion of a perfectly homogeneous mixture. The rich limit was observed around λ=2.0∼2.4. This limit was determined by considering the increase in NOx, and the steep pressure rise. During high load operations is not only the ignition timing but also the combustion rate should be controlled. By comparing the homogeneous charge and direct injection case, the mixture heterogeneity could be found to have an influence on the ignition timing and combustion rate, the engine speed and injection timing also had an influenced on these.

As a method for reducing exhaust emissions from diesel engines, we have experimented on a homogeneous charge diesel combustion technique (HCDC) whereby a portion of fuel is supplied into the intake port to form a homogeneous premixture, this is then fed into the cylinder from the intake port before ignition of the diesel fuel, which is injected directly into the cylinder. Our results have indicated possibilities of substantially reducing both NOx and smoke emissions. If diesel fuel is premixed with air, the premixture under-goes excessively early self-ignition, making it difficult to maintain ignition timing near top dead center and hence limiting the engine operating conditions. While an important target in emission reduction is to realize stable low-emission combustion during a high-load operation, the actual operation of diesel engines mostly involves partial-load conditions.

The use of water injection in a Homogeneous Charge Compression Ignition (HCCI) engine was experimentally investigated. The purpose of this study was to examine whether it is possible to control the ignition timing and slow down the rate of combustion with the use of water injection. The effects of different water flows, air/fuel ratios and inlet pressures were studied for three different fuels, iso-octane, ethanol and natural gas. It is possible to control the ignition timing in a narrow range with the use of water injection, but to the prize of an increase in the already high emissions of unburned hydrocarbons. The CO emission also increased. The NOx emissions, which are very low for HCCI, decreased even more when water injection was applied. The amount of water used was of the magnitude of the fuel flow.

Previous research in our laboratory has shown that NOx emissions can be sharply reduced by PREDIC (PRE-mixed lean DIesel Combustion), in which fuel is injected very early in the compression process. However some points of concern remained unsolved, such as a large increase in THC and CO, higher fuel consumption, and an operating region narrowly limited to partial loads, compared to conventional diesel operation. In this paper, the causes of PREDIC's problem areas were analyzed through engine performance tests and combustion observation with a single cylinder engine, through fuel spray observation with a high-pressure vessel, and through numerical modeling. Subsequently, measurable improvements were achieved on the basis of these analyses. As a result, the ignition and combustion processes were clarified in terms of PREDIC fuel-air mixture formation. Thus, THC and CO emissions could be decreased by adopting a pintle type injection nozzle, or a reduced top-land-crevice piston.

The subject of this paper is the discussion of a non-dimensional combustion model that relies on the concept of mixing controlled combustion (MCC Heat Release Rate) avoiding the detailed description of the individual mixture formation and fuel oxidation processes. For diffusion combustion in today's direct injection diesel engines it can be shown that the rate of heat release (ROHR) is controlled mainly by two items, i.e. the instantaneous fuel mass present in the cylinder charge and the local density of turbulent kinetic energy. Both items can be derived from the injection process, the instantaneous fuel mass being the difference of fuel injected minus fuel burnt and the turbulent kinetic energy being produced mainly by the momentum of the fuel sprays. Following this strategy, the injection process is now understood as the most important controlling factor for the heat release rate.

A premixed compression-ignited (PCI) combustion system, which realizes lean combustion with high efficiency and low emissions, was investigated and its effects and problems were ascertained. With PCI combustion, fuel was injected early on the compression stroke and a premixed lean mixture was formed over a long mixing period. The test engine was operated with self-ignition of this premixed lean mixture. From the results of combustion observation and numerical simulation, a need to prevent the fuel spray from adhering to the cylinder liner and combustion-chamber wall was identified. Consequently, an impinged-spray nozzle with low penetration was made and tested. As a result, an extremely low nitrogen-oxide (NOx) emission level was realized but fuel efficiency was detracted slightly. Also, the engine operating range possible with PCI combustion was found to be limited to partial-load conditions and PCI combustion was found to cause an increase in hydrocarbon (HC) emission.

In the paper some measurement results of pumping loops in a high-speed turbocharged D.I. Diesel engine have been presented with the aim to show how the exhaust blowdown period affects the pumping work. Cylinder pressure can drop deeply under the ambient pressure level during the blowdown period. Though this pressure is increasing during the main exhaust period still it remains below the subsequent intake pressure level. This phenomenon can be attributed to the so-called Kadenacy effect which was recognized and used for scavenging of a two-stroke engine as early as in the 1940's. This effect appeared to be strongly dependent on time of the blowdown period i.e. on the rotational speed. In the paper relationships between thermal efficiency and pumping work have been presented. Furthermore, some measurements of cylinder pressure and calculation results of mass flow during the blowdown and exhaust periods have been analyzed.

Dynamic single range analyzers are designed to cover the wide range of concentrations that once required multiple ranges. The use of single range analyzers is attractive because they can significantly reduce installation costs, gas cylinder charges, and facility storage space. The new technology relies on expansion of the digital dynamic range of the analyzer combined with the availability of a high accuracy gas divider with a 500 to one dilution ratio and a large number of cut points. A series of four MEXA 7000 series bag bench analyzers manufactured by Horiba Instruments, Inc., were evaluated to compare multiple range operation with single range operation. This report describes the operation of these analyzers and summarizes the evaluation methods and results. The evaluation verified the ability of the analyzers to operate in single range mode.

Accurate heat release analysis of cylinder pressure data is a powerful tool used in the development of diesel engines. However, significant errors in the calculated heat release values can occur due to shortcomings in both the experimental measurements and in the heat release model and this can produce misleading results. This paper shows the effect of such common errors on the calculated gross heat release data obtained when analysing simulated and experimental direct injection diesel engine pressure diagrams using a traditional single-zone First Law heat release model. The work reveals that the greatest uncertainty in most cases will be caused by assuming the wrong rate of heat transfer between the cylinder charge and combustion chamber walls. To overcome this limitation, an alternative heat release model is proposed and shown to give very good results over a wide range of operating conditions.

The new generation of emission analyzers, MEXA 7000 series, manufactured by Horiba Instruments, Incorporated, operate as single range instruments. The wide operational range of the new analyzers requires a new calibration/linearization tool, a new gas divider capable of providing more calibration points over a wider dynamic operational range. The operation of the new gas divider (Horiba GDC-703), based on mass flow control technology, provides 40 cut points with a minimum step size of 1/500, or 0.2%, of the calibration gas value. This paper describes the new Horiba gas divider, GDC-700 series. The evaluation proves the gas divider's viability for use in engine and vehicle emissions test laboratories. Extensive sets of data were collected to provide an evaluation of the gas divider over a wide range of operation for measurement linearity, repeatability, and accuracy.