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The effects of EGR on diesel combustion were visually examined in a single-cylinder heavy duty research engine with a low compression ratio, low swirl, a CR fuel injection system and an eight-orifice nozzle. Optical access was primarily obtained through the cylinder head. The effects of EGR were found to be significant. NOx emissions were reduced from over 500 ppm at 0% EGR to 5 ppm at 55% EGR. At higher levels of EGR (approximately 35% or more) there was a loss in efficiency. Constant fuel masses were injected. Results from the optical measurements and global emission data were compared in order to obtain a better understanding of the spray behaviour and mixing process. Optical measurements provide fundamental insights by visualizing air motion and combustion behaviour. The NOx reductions observed might be explained by reductions in oxygen concentration associated with the increases in EGR.

Autoignition of a homogeneous mixture is very sensitive to operating conditions. Therefore fast combustion phasing control is necessary for reliable operation. There are several means to control the combustion phasing of a Homogeneous Charge Compression Ignition (HCCI) engine. This paper presents cycle-to-cycle cylinder individual control results from a six-cylinder HCCI engine using a Variable Valve Actuation (VVA) system. As feedback signal, the crank angle for 50% burned, based on cylinder pressure, is used. Three control structures are evaluated, Model Predictive Control (MPC), Linear Quadratic Gaussian control (LQG) and PID control. In the control design of the MPC and LQG controller, dynamic models obtained by system identification were used. Successful experiments were performed on a port-injected six-cylinder heavy-duty Diesel engine operating in HCCI mode.

The wavelet transform is used in the analysis of the cylinder pressure trace and the ionic current trace of a knocking, single-cylinder, spark ignition engine. Using the wavelet transform offers a significant reduction of mathematical operations when compared with traditional filtering techniques based on the Fourier transform. It is shown that conventional knock analysis in terms of average energy in the time domain (AETD), corresponding to the signal's energy content, and maximum amplitude in the time domain (MATD), corresponding to the maximum amplitude of the bandpass filtered signal, can be applied to both the reconstructed filtered cylinder pressure and the wavelet coefficients. The use of the filter coefficients makes possible a significant additional reduction in calculation effort in comparison with filters based on the windowed Fourier transform.

Unburned hydrocarbon (UHC) and carbon monoxide (CO) emission sources are examined in an optical, light-duty diesel engine operating under low load and engine speed, while employing a highly dilute, partially premixed low-temperature combustion (LTC) strategy. The impact of engine load and charge dilution on the UHC and CO sources is also evaluated. The progression of in-cylinder mixing and combustion processes is studied using ultraviolet planar laser-induced fluorescence (UV PLIF) to measure the spatial distributions of liquid- and vapor-phase hydrocarbon. A separate, deep-UV LIF technique is used to examine the clearance volume spatial distribution and composition of late-cycle UHC and CO. Homogeneous reactor simulations, utilizing detailed chemical kinetics and constrained by the measured cylinder pressure, are used to examine the impact of charge dilution and initial stoichiometry on oxidation behavior.

Thermodynamic power cycles have been shown to provide an excellent method for waste heat recovery (WHR) in internal combustion engines. By capturing and reusing heat that would otherwise be lost to the environment, the efficiency of engines can be increased. This study evaluates the maximum power output of different cycles used for WHR in a heavy duty Diesel engine with a focus on working fluid selection. Typically, only high temperature heat sources are evaluated for WHR in engines, whereas this study also considers the potential of WHR from the coolant. To recover the heat, four types of power cycles were evaluated: the organic Rankine cycle (ORC), transcritical Rankine cycle, trilateral flash cycle, and organic flash cycle. This paper allows for a direct comparison of these cycles by simulating all cycles using the same boundary conditions and working fluids.

Ion current measurements can give information useful for controlling the combustion stability in a multi-cylinder engine. Operation near the dilution limit (air or EGR) can be achieved and it can be optimized individually for the cylinders, resulting in a system with better engine stability for highly diluted mixtures. This method will also compensate for engine wear, e.g. changes in volumetric efficiency and fuel injector characteristics. Especially in a port injected engine, changes in fuel injector characteristics can lead to increased emissions and deteriorated engine performance when operating with a closed-loop lambda control system. One problem using the ion-current signal to control engine stability near the lean limit is the weak signal resulting in low signal to noise ratio. Measurements presented in this paper were made on a turbocharged 9.6 liter six cylinder natural gas engine with port injection.

Exhaust Gas Recirculation, EGR, is one of the most effective means of reducing NOx emissions from diesel engines and is likely to be used in order to meet future emissions standards. Exhaust gases can either be used to replace some of the air that enters the engine or can be added to the intake flow. The former case has been studied in this paper. One advantage of air replacement is that the exhaust mass flow is reduced in addition to the decreased NOx formation. The objective of this study has been to take a closer look at the factors affecting NOx emissions at different EGR rates. This is done by combining heat release analysis, based on measured pressure traces and NO formation in a multi zone combustion model. The model used is an improved version of an earlier presented model [1]. One feature in the new model is the possibility to separate the NO formation during the premixed combustion from NO formed during the diffusive combustion.

The different roles played by small and large eddies in engine combustion were studied. Experiments compared natural gas combustion in a converted, single cylinder Volvo TD 102 engine and in a 125 mm cubical cell. Turbulence is used to enhance flame growth, ideally giving better efficiency and reduced cyclic variation. Both engine and test cell results showed that flame growth rate correlated best with the level of high frequency, small eddy turbulence. The more effective, small eddy turbulence also tended to lower cyclic variations. Large scales and bulk flows convected the flame relative to cool surfaces and were most important to the initial flame kernel.

This study is focused on the effect of different valve strategies on the in-cylinder flow and combustion A conventional four-valve pentroof engine was modified to enable optical access to the combustion chamber To get information on the flow, a two-component LDV system was applied The combustion was monitored by the use of cylinder pressure in a one-zone heat release model The results show that the flow in the cylinder with the valves operating in the standard configuration has an expected tumble characteristic In this case the high frequency turbulence is homogeneous and has a peak approximately 20 CAD BTDC With one valve deactivated, the flow shows a swirling pattern The turbulence is then less homogeneous but the level of turbulence is increased When the single inlet valve was phased late against the crankshaft dramatic effects on the flow resulted The late inlet valve opening introduced a low cylinder pressure before the valve opened The high pressure difference across the valve introduced a high-velocity jet into the cylinder Turbulence was increased by a factor of two by this operational mode When two inlet valves were used, a reduction of turbulence resulted from a very late inlet cam phase

2-D LDV measurements were performed on two different cylinder designs in a fired two-stroke engine running with wide-open throttle at 9000 rpm. The cylinders examined were one with open transfer channels and one with cup handle transfer channels. Optical access to the cylinder was achieved by removing the silencer and thereby gain optical access through the exhaust port. No addition of seeding was made, since the fuel droplets were not entirely vaporized as they entered the cylinder and thus served as seeding. Results show that the loop-scavenging effect was poor with open transfer channels, but clearly detectable with cup handle channels. The RMS-value, “turbulence”, was low close to the transfer ports in both cylinders, but increased rapidly in the middle of the cylinder. The seeding density was used to obtain information about the fuel concentration in the cylinder during scavenging.

It is generally accepted that knocking combustion influences the heat transfer in SI engines. However, the effects of heat transfer on the onset of knock is still not clear due to lack of experimental data of the thermal boundary layer close to the combustion chamber wall. This paper presents measurements of the temperature in the thermal boundary layer under knocking and non-knocking conditions. The temperature was measured using dual-broadband rotational Coherent anti-Stokes Raman Spectroscopy (CARS). Simultaneous time-resolved measurements of the cylinder pressure, at three different locations, and the heat flux to the wall were carried out. Optical access to the region near the combustion chamber wall was achieved by using a horseshoe-shaped combustion chamber with windows installed in the rectangular part of the chamber. This arrangement made CARS temperature measurements close to the wall possible and results are presented in the range 0.1-5 mm from the wall.

Heat transfer to the walls of the combustion chamber is increased by engine knock. In this study the influence of knock onset and knock intensity on the heat flux is investigated by examining over 10 000 individual engine cycles with a varying degree of knock. The heat transfer to the walls was estimated by measuring the combustion chamber wall temperature in an SI engine under knocking conditions. The influence of the air-fuel ratio and the orientation of the oscillating cylinder pressure-relative to the combustion chamber wall-were also investigated. It was found that knock intensities above 0.2 Mpa influenced the heat flux. At knock intensities above 0.6 Mpa, the peak heat flux was 2.5 times higher than for a non-knocking cycle. The direction of the oscillations did not affect the heat transfer.

A naturally aspirated in-line six-cylinder 2.9-litre Volvo engine is operated in Homogeneous Charge Compression Ignition (HCCI) mode, using camshafts with low lift and short duration generating negative valve overlap. This implementation requires only minor modifications of the standard SI engine and allows SI operation outside the operating range of HCCI. Standard port fuel injection is used and pistons and cylinder head are unchanged from the automotive application. A heat exchanger is utilized to heat or cool the intake air, not as a means of combustion control but in order to simulate realistic variations in ambient temperature. The combustion is monitored in real time using cylinder pressure sensors. HCCI through negative valve overlap is recognized as one of the possible implementation strategies of HCCI closest to production. However, for a practical application the intake temperature will vary both geographically and from time to time.

This paper discusses the effects of cooled EGR on a turbo charged multi cylinder HCCI engine. A six cylinder, 12 liter, Scania D12 truck engine is modified for HCCI operation. It is fitted with port fuel injection of ethanol and n-heptane and cylinder pressure sensors for closed loop combustion control. The effects of EGR are studied in different operating regimes of the engine. During idle, low speed and no load, the focus is on the effects on combustion efficiency, emissions of unburned hydrocarbons and CO. At intermediate load, run without turbocharging to achieve a well defined experiment, combustion efficiency and emissions from incomplete combustion are still of interest. However the effect on NOx and the thermodynamic effect on thermal efficiency, from a different gas composition, are studied as well. At high load and boost pressure the main focus is NOx emissions and the ability to run high mean effective pressure without exceeding the physical constraints of the engine.

The main purpose of this study is to investigate the effects of exhaust gases on different combustion modes in DI, Direct Injection, compression ignited engines in terms of combustion efficiency and emission formations. The conventional parametric Φ -T (Equivalence Ratio-Temperature) emission map analysis has been extended by constructing the transient maps for different species characterizing the combustion and emission formation processes. The results of the analysis prove the efficiency of different combustion modes when EGR loads and injection scenarios.

In an attempt to extend the upper load limit for Homogeneous Charge Compression Ignition (HCCI), supercharging in combination with Exhaust Gas Recirculation (EGR) have been applied. Two different boost pressures were used, 1.1 bar and 1.5 bar. High EGR rates were used in order to reduce the combustion rate. The highest obtained IMEP was 16 bar. This was achieved with the higher boost pressure, at close to stoichiometric conditions and with approximately 50 % EGR. Natural gas was used as the main fuel. In the case with the higher boost pressure, iso-octane was used as pilot fuel, to improve the ignition properties of the mixture. This made it possible to use a lower compression ratio and thereby reducing the maximum cylinder pressure. The tests were performed on a single cylinder engine operated at low speed (1000 rpm). The test engine was equipped with a modified cylinder head, having a Variable Compression Ratio (VCR) mechanism.

Styrene, or ethylbenzene, is mainly used as a monomer for the production of polymers, most notably Styrofoam. In the synthetis of styrene, the feedstock of benzene and ethylene is converted into aromatic oxygenates such as benzaldehyde, 2-phenyl ethanol and acetophenone. Benzaldehyde and phenyl ethanol are low value side streams, while acetophenone is a high value intermediate product. The side streams are now principally rejected from the process and burnt for process heat. Previous in-house research has shown that such aromatic oxygenates are suitable as diesel fuel additives and can in some cases improve the soot-NOx trade-off. In this study acetophenone, benzaldehyde and 2-phenyl ethanol are each added to commercial EN590 diesel at a ratio of 1:9, with the goal to ascertain whether or not the lower value benzaldehyde and 2-phenyl ethanol can perform on par with the higher value acetophenone. These compounds are now used in pure form.

Homogeneous Charge Compression Ignition (HCCI) has a great potential for low NOx emissions but problems with emissions of unburned hydrocarbons (HC). One way of reducing the HC is to use direct injection. The purpose of this paper is to present experimental data on the trade off between NOx and HC. Injection timing, injection pressure and nozzle configuration all effect homogeneity of the mixture and thus the NOx and HC emissions. The engine studied is a single cylinder version of a Scania D12 that represents a modern heavy-duty truck size engine. A common rail (CR) system has been used to control injection pressure and timing. The combustion using injectors with different nozzle hole diameters and spray angle, both colliding and non-colliding, has been studied. The NOx emission level changes with start of injection (SOI) and the levels are low for early injection timing, increasing with retarded SOI. Different injectors produce different NOx levels.

2D-LDV-measurements were made on the flow from one transfer channel into the cylinder in a small two-stroke SI engine. The LDV measuring volume was located just outside the transfer port. The engine was a carburetted piston-ported crankcase compression chainsaw engine and it was run with wide open throttle at 9000 RPM. The muffler was removed to enable access into the cylinder. No additional seeding was used; the fuel and/or oil was not entirely vaporized as it entered the cylinder. Very high velocities (-275 m/s) were detected in the beginning of the scavenging phase. The horizontal velocity was, during the whole scavenging phase, higher than the vertical.

Soot formation and oxidation are complex and competing processes during diesel combustion. The balance between the two processes and their history determines engine-out soot values. Besides the efforts to lower soot formation with measures to influence the flame lift-off distance for example or to use HCCI-combustion, enhancement of late soot oxidation is of equal importance for low-λ diffusion-controlled low emissions combustion with EGR. The purpose of this study is to investigate soot oxidation in a heavy duty diesel engine by statistical analysis of engine data and in-cylinder endoscopic high speed photography together with CFD simulations with a main focus on large scale in-cylinder gas motion. Results from CFD simulations using a detailed soot model were used to reveal details about the soot oxidation.