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The local equivalence ratio, Φ, was measured in fuel jets using laser-induced spontaneous Raman scattering in an optical heavy duty diesel engine. The measurements were performed at 1200 rpm and quarter load (6 bar IMEP). The objective was to study factors influencing soot formation, such as gas entrainment and lift-off position, and to find correlations with engine-out particulate matter (PM) levels. The effects of nozzle hole size, injection pressure, inlet oxygen concentration, and ambient density at TDC were studied. The position of the lift–off region was determined from OH chemiluminescence images of the flame. The liquid penetration length was measured with Mie scattering to ensure that the Raman measurement was performed in the gaseous part of the spray. The local Φ value was successfully measured inside a fuel jet. A surprisingly low correlation coefficient between engine-out PM and the local Φ in the reaction zone were observed.

The operating range in HCCI mode is limited by the excessive pressure rise rate and therefore high combustion induced noise. The HCCI range can be extended with turbocharging which enables increased dilution of the charge and thus a reduction of combustion noise. When the engine is turbocharged the intake charge will have a high temperature at increased boost pressure and can then be regulated in a cooling circuit. Limitations and benefits are examed at 2250 rpm and 400 kPa indicated mean effective pressure. It is shown that combustion stability, combustion noise and engine efficiency have to be balanced since they have optimums at different intake temperatures and combustion timings. The span for combustion timings with high combustion stability is narrower at some intake temperatures and the usage of external EGR can improve the combustion stability. It is found that the standard deviation of combustion timing is a useful tool for evaluating cycle to cycle variations.

The soot distribution as function of ambient O₂ mole fraction in a heavy-duty diesel engine was investigated at low load (6 bar IMEP) with laser-induced incandescence (LII) and natural luminosity. A Multi-YAG laser system was utilized to create time-resolved LII using 8 laser pulses with a spacing of one CAD with detection on an 8-chip framing camera. It is well known that the engine-out smoke level increases with decreasing oxygen fraction up to a certain level where it starts to decrease again. For the studied case the peak occurred at an O₂ fraction of 11.4%. When the oxygen fraction was decreased successively from 21% to 9%, the initial soot formation moved downstream in the jet. At the lower oxygen fractions, below 12%, no soot was formed until after the wall interaction. At oxygen fractions below 11% the first evidence of soot is in the recirculation zone between two adjacent jets.

Using alternative fuels like Natural Gas (NG) has shown good potentials on heavy duty engines. Heavy duty NG engines can be operated either lean or stoichiometric diluted with EGR. Extending Dilution limit has been identified as a beneficial strategy for increasing efficiency and decreasing emissions. However dilution limit is limited in these types of engines because of the lower burnings rate of NG. One way to extend the dilution limit of a NG engine is to run the engine on Hythane (natural gas + some percentage hydrogen). Previously effects of Hythane with 10% hydrogen by volume in a stoichiometric heavy duty NG engine were studied and no significant changes in terms of efficiency and emissions were observed. This paper presents results from measurements made on a heavy duty 6-cylinder NG engine. The engine is operated with NG and Hythane with 25% hydrogen by volume and the effects of these fuels on the engine performance are studied.

High-speed OH chemiluminescence imaging is used to measure the lift-off length of diesel sprays in an optical heavy-duty diesel engine of 2 L displacement operated at 1200 rpm and 5 bar IMEP. Stereoscopic images are acquired at two different wavelengths (310 and 330 nm). Subtraction of pairwise images helps reducing the background coming from natural soot incandescence in the OH chemiluminescence images. Intake air temperature (343 to 403 K), motored top dead center density (18 to 22 kg/m3), fuel injection pressure (150 to 250 MPa), intake oxygen concentration (17 to 21 %vol) and nozzle diameter (0.1 and 0.14 mm) are varied and a nonlinear regression model is derived from the experimental results to describe stabilized lift-off length as function of the experimental factors. The lift-off length follows the general trends that are known from spray vessel investigations, but the strength of the dependence on certain variables deviates strongly from those studies.

In the last couple of decades, countries have enacted new laws concerning environmental pollution caused by heavy-duty commercial and passenger vehicles. This is done mainly in an effort to reduce smog and health impacts caused by the different pollutions. One of the legislated pollutions, among a wide range of regulated pollutions, is nitrogen oxides (commonly abbreviated as NOx). The SCR (Selective Catalytic Reduction) was introduced in the automotive industry to reduce NOx emissions leaving the vehicle. The basic idea is to inject a urea solution (AdBlue™) in the exhaust gas before the gas enters the catalyst. The optimal working temperature for the catalyst is somewhere in the range of 300 to 400 °C. For the reactions to occur without a catalyst, the gas temperature has to be at least 800 °C. These temperatures only occur in the engine cylinder itself, during and after the combustion.

The major challenge of the post-processing of soot aggregates in transmission electron microscope (TEM) images is the detection of soot primary particles that have no clear boundaries, vary in size within the fractal aggregates, and often overlap with each other. In this study, we propose an automated detection code for primary particles implementing the Canny Edge Detection (CED) and Circular Hough Transform (CHT) on pre-processed TEM images for particle edge enhancement using unsharp filtering as well as image inversion and self-subtraction. The particle detection code is tested for soot TEM images obtained at various ambient and injection conditions, and from five different combustion facilities including three constant-volume combustion chambers and two diesel engines.

Soot emissions from diesel engines are the net result of two competing processes: soot formation and soot oxidation. Previous studies have shown poor correlation between soot formation rates and the soot emissions. This article presents a systematic study of a number of parameters affecting soot oxidation rate and how it correlates with the soot emissions. An optical heavy-duty engine is used in conjunction with a laser extinction setup in order to collect time resolved data of the soot concentration in the cylinder during the expansion stroke. Laser extinction is measured using a red (685 nm) laser beam, which is sent vertically through the cylinder and modulated to produce 10 pulses per crank angle degree. Information is obtained about the amount of soot formed and the soot oxidation rate. The parameters studied are the motored density at top dead center (TDC), motored temperature at TDC, injection pressure, engine speed, swirl level and injector orifice diameter.

The focus has recently been directed towards the engine out soot from Diesel engines. Running an engine in PPC (Partially Premixed Combustion) mode has a proven tendency of reducing these emissions significantly. In addition to combustion strategy, several studies have suggested that using alcohol fuels aid in reducing soot emissions to ultra-low levels. This study analyzes and compares the characteristics of PM emissions from naphtha gasoline PPC, ethanol PPC, methanol PPC and methanol diffusion combustion in terms of soot mass concentration, number concentration and particle size distribution in a single cylinder Scania D13 engine, while varying the intake O2. Intake temperature and injection pressure sweeps were also conducted. The fuels emitting the highest mass concentration of particles (Micro Soot Sensor) were gasoline and methanol followed by ethanol. The two alcohols tested emitted nucleation mode particles only, whereas gasoline emitted accumulation mode particles as well.

The effects of injection pressure and swirl ratio on the in-cylinder soot oxidation are studied using simultaneous PLIF imaging of OH and LII imaging of soot in an optical diesel engine. Images are acquired after the end of injection in the recirculation zone between two adjacent diesel jets. Scalars are extracted from the images and compared with trends in engine-out soot emissions. The soot emissions decrease monotonically with increasing injection pressure but show a non-linear dependence on swirl ratio. The total amount of OH in the images is negatively correlated with the soot emissions, as is the spatial proximity between the OH and soot regions. This indicates that OH is an important soot oxidizer and that it needs to be located close to the soot to perform this function. The total amount of soot in the images shows no apparent correlation with the soot emissions, indicating that the amount of soot formed is a poor predictor of the emission trends.

Model-based analysis of in-cylinder pressure sensor signals has been a key component for internal combustion engine research, diagnostics and controller development during the past decades. This analysis is often based on simple thermodynamic models of the in-cylinder processes. In order for the analysis to give accurate results, the models need to be sufficiently calibrated. This paper investigates the use of the extended Kalman filter and the particle filter for the purpose of online estimation of top-dead-center offset, a convective heat-transfer coefficient and cylinder-wall temperature in a Gatowski heat-release model. Simulation results show that the filters are consistent in estimating the true parameters, that the assumed model uncertainty and heat-release noise density works as filter tuning parameters. The filters were found to be sensitive to errors on pressure-sensor offset and the cylinder compression ratio.

Fumigation was studied in a 12 L six-cylinder heavy-duty engine. Port-injected ethanol was ignited with a small amount of diesel injected into the cylinder. The setup left much freedom for influencing the combustion process, and the aim of this study was to find operation modes that result in a combustion resembling that of a homogeneous charge compression ignition (HCCI) engine with high efficiency and low NOx emissions. Igniting the ethanol-air mixture using direct-injected diesel has attractive properties compared to traditional HCCI operation where the ethanol is ignited by pressure alone. No preheating of the mixture is required, and the amount of diesel injected can be used to control the heat release rate. The two fuel injection systems provide a larger flexibility in extending the HCCI operating range to low and high loads. It was shown that cylinder-to-cylinder variations present a challenge for this type of combustion.

Partially Premixed Combustion (PPC) has shown its potential by combining high combustion controllability with emission characteristics that are close to those of an HCCI engine. In order to get PPC the ignition delay needs to be long enough for the fuel and air to mix prior to combustion. This can be achieved by injecting the fuel sufficiently early while running with high EGR. In order to find out where and how PPC occurs a map that shows the changes in combustion characteristics with injection timing and EGR was created. The combustion characteristics were studied in a six cylinder heavy duty engine where the Start of Injection (SOI) was swept from early to late injection over a wide range of EGR levels. The emissions were monitored during the sweeps and in the most promising regions, with low emissions and high efficiency, additional changes in injection pressure and engine speed were applied to get a more versatile picture of the combustion.

High EGR rates combined with turbocharging has been identified as a promising way to increase the maximum load and efficiency of heavy duty spark ignition engines. With stoichiometric conditions a three way catalyst can be used which means that regulated emissions can be kept at very low levels. Obtaining reliable spark ignition is difficult however with high pressure and dilution. There will be a limit to the amount of EGR that can be tolerated for each operating point. Open loop operation based on steady state maps is difficult since there is substantial dynamics both from the turbocharger and from the wall heat interaction. The proposed approach applies standard closed loop lambda control for controlling the overall air/fuel ratio for a heavy duty 6-cylinder port injected natural gas engine. A closed loop load control is also applied for keeping the load at a constant level when using EGR.

Laser-Induced Incandescence (LII) has traditionally been considered a straightforward and reliable optical diagnostic technique for in-cylinder soot measurements. As a result, it is nowadays even possible to buy turn-key LII measurement systems. During recent years, however, attention has been drawn to a number of unresolved challenges with LII. Many of these are relevant mostly for particle sizing using time-resolved LII, but also two-dimensional soot volume fraction measurements are affected, especially in regions with high soot concentrations typically found in combustion engines. In this work the focus is on the specific challenges involved in performing high-repetition rate measurements with LII in diesel engines. All the mentioned issues might not be possible to overcome but they should nevertheless be known and their potential impact should be considered.

Post-injection strategies aimed at reducing engine-out emissions of unburned hydrocarbons (UHC) were investigated in an optical heavy-duty diesel engine operating at a low-load, low-temperature combustion (LTC) condition with high dilution (12.7% intake oxygen) where UHC emissions are problematic. Exhaust gas measurements showed that a carefully selected post injection reduced engine-out load-specific UHC emissions by 20% compared to operation with a single injection in the same load range. High-speed in-cylinder chemiluminescence imaging revealed that without a post injection, most of the chemiluminescence emission occurs close to the bowl wall, with no significant chemiluminescence signal within 27 mm of the injector. Previous studies have shown that over-leaning in this near-injector region after the end of injection causes the local equivalence ratio to fall below the ignitability limit.

In the automotive industry, the piezo-based in-cylinder pressure sensor is getting commercialized and used in production vehicles. For example, the pressure sensor offers the opportunity to design algorithms for estimation of engine emissions, such as soot and NO , during a combustion cycle. In this paper a zero-dimensional NO model for a diesel engine is implemented that will be used in real time. The model is based on the thermal NO formation and the Zeldovich mechanism using two non-geometrical zones: burned and unburned zone. The influence of EGR on combustion temperature was modeled using a well-known thermodynamic identity where specific heat at constant pressure is included. Specific heat will vary with temperature and the gas composition. The model was implemented in LabVIEW using tools specific for an FPGA (Field-Programmable Gate Array).

Gasoline partially premixed combustion (PPC) has the potential of high efficiency and simultaneous low soot and NOx emissions. Running the engine in PPC mode with high octane number fuels has the advantage of a longer premix period of fuel and air which reduces soot emissions. The problem is the ignitability at low load and idle operating conditions. In a previous study it was shown that it is possible to use NVO to improve combustion stability and combustion efficiency at operating conditions where available boosted air is assumed to be limited. NVO has the disadvantage of low net indicated efficiency due to heat losses from recompressions of the hot residual gases. An alternative to NVO is the rebreathing valve strategy where the exhaust valves are reopened during the intake stroke. The net indicated efficiency is expected to be higher with the rebreathing strategy but the question is if similar improvements in combustion stability can be achieved with rebreathing as with NVO.

This paper investigates the FPGA resources for the implementation of in-cycle closed-loop combustion control algorithms. Closed-loop combustion control obtains feedback from fast in-cylinder pressure measurements for accurate and reliable information about the combustion progress, synchronized with the flywheel encoder. In-cycle combustion control requires accurate and fast computations for their real-time execution. A compromise between accuracy and computation complexity must be selected for an effective combustion control. The requirements on the signal processing (evaluation rate and digital resolution) are investigated. A common practice for the combustion supervision is to monitor the heat release rate. For its calculation, different methods for the computation of the cylinder volume and heat capacity ratio are compared. Combustion feedback requires of virtual sensors for the misfire detection, burnt fuel mass and pressure prediction.

Power supply systems play a very important role in applications of everyday life. Mainly, for low power generation, there are two ways of producing energy: electrochemical batteries and small engines. In the last few years many improvements have been carried out in order to obtain lighter batteries with longer duration but unfortunately the energy density of 1 MJ/kg seems to be an asymptotic value. If the energy source is an organic fuel with an energy density of around 29 MJ/kg and a minimum overall efficiency of only 3.5%, this device can surpass the batteries. Nowadays the most efficient combustion process is HCCI combustion which is able to combine high energy conversion efficiency and low emission levels with a very low fuel consumption. In this paper, an investigation has been carried out concerning the effects of the compression ratio on the performance and emissions of a mini, Vd = 4.11 [cm3], HCCI engine fueled with diethyl ether.