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Increased research is being driven by the automotive industry facing challenges, requiring to comply with both current and future emissions legislation, and to lower the fuel consumption. The reason for this legislation is to restrict the harmful pollution which every year causes 3.3 million premature deaths worldwide [1]. One factor that causes this pollution is NOx emissions. NOx emission legislation has been reduced from 8 g/kWh (Euro I) down to 0.4 g/kWh (Euro VI) and recently new legislation for ammonia slip which increase the challenge of exhaust aftertreatment with a SCR system. In order to achieve a good NOx conversion together with a low slip of ammonia, small droplets of Urea solution needs to be injected which can be rapidly evaporated and mixed into the flow of exhaust gases.

The paper describes a novel method for calculating the residual gas fraction and the trapping efficiency in a 2 stroke engine. Assuming one dimensional compressible flow through the inlet and exhaust ports, the method estimates the instantaneous mass flowing in and out from the combustion chamber; later the residual gas fraction and trapping efficiency are estimated combining together the perfect displacement and perfect mixing scavenging models. It is assumed that when the intake port opens, the fresh mixture is pushing out the burned charge without any mixing and after a multiple of the time needed for the largest eddy to perform one rotation, the two gasses are instantly mixed up together and expelled. The result is a very simple algorithm that does not require much computational time and is able to estimate with high level of precision the trapping efficiency and the residual gas fraction in 2 stroke engines.

To provide insights into the fundamental characteristics of pre-chamber combustion engines, the ignition of lean premixed CH4/air due to hot gas jets initiated by a passive narrow throated pre-chamber in a heavy-duty engine was studied computationally. A twelve-hole pre-chamber geometry was investigated using CONVERGETM software. The numerical model was validated against the experimental results. To elucidate the main-chamber ignition mechanism, the spark plug location and spark timing were varied, resulting in different pressure gradient during turbulent jet formation. Different ignition mechanisms were observed for turbulent jet ignition of lean premixed CH4/air, based on the geometry effect. Ignition behavior was classified into the flame and jet ignition depending on the significant presence of hot active radicals. The jet ignition, mainly due to hot product gases was found to be advanced by the addition of a small concentration of radicals.

In this paper a fast NOx model is presented which can be used for engine optimization, aftertreatment control or virtual mapping. A cylinder pressure trace is required as input data. High calculation speed is obtained by using table interpolation to calculate equilibrium temperatures and species concentrations. Test data from a single-cylinder engine and from a complete six-cylinder engine have been used for calibration and validation of the model. The model produces results of good agreement with emission measurements using approximately 50 combustion product zones and a calculation time of one second per engine cycle. Different compression ratios, EGR rates, injection timing, inlet pressures etc. were used in the validation tests.

Heavy-duty vehicles face increasing demands of emission regulations. Reduced carbon-dioxide (CO2) emission targets motivate decreased fuel consumption for fossil fuel engines. Increased engine efficiency contributes to lower fuel consumption and can be achieved by lower heat transfer, friction and exhaust losses. The double compression expansion engine (DCEE) concept achieves higher efficiency, as it utilizes a split-cycle approach to increase the in-cylinder pressure and recover the normally wasted exhaust energy. However, the DCEE concept suffers heat losses from the high-pressure approach. This study utilizes up to three injectors to reduce the wall-gas temperature gradient rendering lower convective heat losses. The injector configuration consists of a standard central injector and two side-injectors placed at the rim of the bowl. An increased distance from side-injector to the wall delivered lower heat losses by centralizing hot gases in the combustion chamber.

Due to stringent emission standards, the demand for higher efficiency engines has been unprecedentedly high in recent years. Among several existing combustion modes, pre-chamber spark ignition (PCSI) emerges to be a potential candidate for high-efficiency engines. Research on the pre-chamber concept exhibit higher indicated efficiency through lean limit extension while maintaining the combustion stability. In this study, a unique pre-chamber geometry was tested in a single-cylinder heavy-duty engine at low load lean conditions. The geometry features a narrow throat, which was designed to be packaged inside a commercial diesel injector pocket. The pre-chamber was fueled with methane while the main chamber was supplied with an ethanol/air mixture.

An experimental study of a glow plug engine combustion process has been performed by applying chemiluminescence imaging. The major intent was to understand what kind of combustion is present in a glow plug engine and how the combustion process behaves in a small volume and at high engine speed. To achieve this, images of natural emitted light were taken and filters were applied for isolating the formaldehyde and hydroxyl species. Images were taken in a model airplane engine, 4.11 cm3, modified for optical access. The pictures were acquired using a high speed camera capable of taking one photo every second or fourth crank angle degree, and consequently visualizing the progress of the combustion process. The images were taken with the same operating condition at two different engine speeds: 9600 and 13400 rpm. A mixture of 65% methanol, 20% nitromethane and 15% lubricant was used as fuel.

An experimental study of the Homogeneous Charge Compression Ignition (HCCI) combustion process has been conducted by using chemiluminescence imaging. The major intent was to characterize the flame structure and its transient behavior. To achieve this, time resolved images of the naturally emitted light were taken. Emitted light was studied by recording its spectral content and applying different filters to isolate species like OH and CH. Imaging was enabled by a truck-sized engine modified for optical access. An intensified digital camera was used for the imaging. Some imaging was done using a streak-camera, capable of taking eight arbitrarily spaced pictures during a single cycle, thus visualizing the progress of the combustion process. All imaging was done with similar operating conditions and a mixture of n-heptane and iso-octane was used as fuel. Some 20 crank angles before Top Dead Center (TDC), cool flames were found to exist.

The emission control in heavy-duty vehicles today is based on predefined injection strategies and after-treatment systems such as SCR (selective catalytic reduction) and DPF (diesel particulate filter). State-of-the-art engine control is presently based on cycle-to-cycle resolution. The introduction of the crank angle resolved pressure measurement, from a piezo-based pressure sensor, enables the possibility to control the fuel injection based on combustion feedback while the combustion is occurring. In this paper a study is presented on the possibility to control NOx (nitrogen oxides) formation with a crank angle resolved NOx estimator as feedback. The estimator and the injection control are implemented on an FPGA (Field-Programmable Gate Array) to manage the inherent time constraints. The FPGA is integrated with the rest of the engine control system for injection control and measurement.

Stringent emission regulations and the anticipated climate change call for a paradigm shift in the design of the conventional internal combustion engines. One way to combat this problem is oxy-fuel combustion in which the combustion products are mainly water vapor and carbon dioxide. Water vapor can be easily separated by condensation and carbon dioxide is then easily captured and stored. However, many technical challenges are associated with this mode of combustion. There are many challenges facing oxy-fuel combustion before it find its way to commercial production especially for internal combustion engines. One such challenge is the relatively high temperature of the oxy-fuel combustion. A solution to this problem is the recirculation of the generated CO2 to moderate the in-cylinder temperature. Therefore, careful study of the effect of recirculating the CO2 back to combustion chamber is needed before the implementation of such a concept.

A 6-cylinder truck engine is modified for turbo charged dual fuel Homogeneous Charge Compression Ignition (HCCI) engine operation. Two different fuels, ethanol and n-heptane, are used to control the ignition timing. The objective of this study is to demonstrate high load operation of a full size HCCI engine and to discuss some of the typical constraints associated with HCCI operation. This study proves the possibility to achieve high loads, up to 16 bar Brake Mean Effective Pressure (BMEP), and ultra low NOx emissions, using turbo charging and dual fuel. Although the system shows great potential, it is obvious that the lack of inlet air pre heating is a drawback at low loads, where combustion efficiency suffers. At high loads, the low exhaust temperature provides little energy for turbo charging, thus causing pump losses higher than for a comparable diesel engine. Design of turbo charger therefore, is a key issue in order to achieve high loads in combination with high efficiency.

A Scania 13 1 engine modified for single cylinder operations was run using nine fuels in the boiling point range of gasoline, but very different octane number, together with PRF20 and MK1-diesel. The eleven fuels were tested in a load sweep between 5 and 26 bar gross IMEP at 1250 rpm and also at idle (2.5 bar IMEP, 600 rpm). The boost level was proportional to the load while the inlet temperature was held constant at 303 K. For each fuel the load sweep was terminated if the ignitibility limit was reached. A lower load limit of 15 and 10 bar gross IMEP was found with fuels having an octane number range of 93-100 and 80-89 respectively, while fuels with an octane number below 70 were able to run through the whole load range including idle. A careful selection of boost pressure and EGR in the previously specified load range allowed achieving a gross indicated efficiency between 52 and 55% while NOx ranged between 0.1 and 0.5 g/kWh.

An air hybrid is a vehicle with an ICE modified to also work as an air compressor and air motor. The engine is connected to two air reservoirs, normally the atmosphere and a high pressure tank. The main benefit of such a system is the possibility to make use of the kinetic energy of the vehicle otherwise lost when braking. The main difference between the air hybrid developed in this paper and earlier air hybrid concepts is the introduction of a pressure tank that substitutes the atmosphere as supplier of low air pressure. By this modification, a very high torque can be achieved in compressor mode as well as in air motor mode. A model of an air hybrid with two air tanks was created using the engine simulation code GT-Power. The results from the simulations were combined with a driving cycle to estimate the reduction in fuel consumption.

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 novel wave-shaped bowl piston geometry design with protrusions has been proved in previous studies to enhance late-cycle mixing and therefore significantly reduce soot emissions and increase engine thermodynamic efficiency. The wave-shaped piston is characterized by the introduction of evenly spaced protrusions around the inner wall of the bowl, with a matching number with the number of injection holes, i.e., flames. The interactions between adjacent flames strongly affect the in-cylinder flow and the wave shape is designed to guide the near-wall flow. The flow re-circulation produces a radial mixing zone (RMZ) that extends towards the center of the piston bowl, where unused air is available for oxidation promotion. The waves enhance the flow re-circulation and thus increase the mixing intensity of the RMZ.

In this study, the authors investigated the effect of fuel properties on the combustion characteristics by employing methane, methanol, ethanol, and primary reference fuels (PRFs) as the main chamber fuel while using methane for the pre-chamber. Global excess air ratios (λ) from 1.6 to lean limit were tested, while 13% of total fuel energy supplied to the engine was delivered via the pre-chamber. The gaseous methane was injected into the pre-chamber at the gas exchange top-dead-center (TDC). Port fuel injection was tested with both open and closed inlet valves. The pre-chamber assembly was designed to fit into the diesel injector pocket of the base engine, which resulted in a narrow throat diameter of 3.3 mm. The combustion stability limit was set at 5% of the coefficient of variation of gross IMEP, and the knock intensity limit was set at 10 bar. GT-Power software was used to estimate the composition of pre-chamber species and was used in heat release analysis of the two chambers.

When applying high amount of EGR (exhaust gas recirculation) in Partially Premixed Combustion (PPC) using diesel fuel, an increase in soot emission is observed as a penalty. To better understand how EGR affects soot particles in the cylinder, a fast gas sampling technique was used to draw gas samples directly out of the combustion chamber in a Scania D13 heavy duty diesel engine. The samples were characterized on-line using a scanning mobility particle sizer for soot size distributions and an aethalometer for black carbon (soot) mass concentrations. Three EGR rates, 0%, 56% and 64% were applied in the study. It was found that EGR reduces both the soot formation rate and the soot oxidation rate, due to lower flame temperature and a lower availability of oxidizing agents. With higher EGR rates, the peak soot mass concentration decreased. However, the oxidation rate was reduced even more.

Fuel effects on ignition delay and low temperature reactions (LTR) during partially premixed combustion (PPC) were analyzed using Design of Experiments (DoE). The test matrix included seventeen mixtures of n-heptane, isooctane, toluene and ethanol covering a broad range of ignition quality and fuel chemistry. Experiments were performed on a light-duty diesel engine at 8 bar IMEPg, 1500 rpm with a variation in combustion phasing, inlet oxygen concentration and injection pressure. A single injection strategy was used and the start of injection and injection duration were adjusted to achieve the desired load and combustion phasing. The experimental data show that fuels with higher Research Octane Number (RON) values generally produced longer ignition delays. In addition, the alcohol content had significantly stronger effect on ignition delay than the aromatic content.

This paper illustrates the applicability of a sequential fluid mechanics, multi-zone chemical kinetics model to analyze HCCI experimental data for two combustion chamber geometries with different levels of turbulence: a low turbulence disc geometry (flat top piston), and a high turbulence square geometry (piston with a square bowl). The model uses a fluid mechanics code to determine temperature histories in the engine as a function of crank angle. These temperature histories are then fed into a chemical kinetic solver, which determines combustion characteristics for a relatively small number of zones (40). The model makes the assumption that there is no direct linking between turbulence and combustion. The multi-zone model yields good results for both the disc and the square geometries. The model makes good predictions of pressure traces and heat release rates.

This article deals with study of ionization current sensing technique's signal characteristics while operating with pre-chamber spark plug to achieve plasma jet ignition in a 6 cylinder 9 liter turbo-charged natural gas engine under EGR and excess air dilution. Unlike the signal with conventional spark plug which can be divided into distinct chemical and thermal ionization peaks, the signal with pre-chamber spark plug shows a much larger first peak and a negligible second peak thereafter. Many studies in past have found the time of second peak coinciding with the time of maximum cylinder pressure and this correlation has been used as an input to combustion control systems but the absence of second peak makes application of this concept difficult with pre-chamber spark plug.