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Increasingly stringent pollutant and CO2 emission standards require the car manufacturers to investigate innovative solutions to further improve the fuel economy and environmental impact of their fleets. Nowadays, NOx emissions standards are stringent for spark-ignition (SI) internal combustion engines (ICEs) and many techniques are investigated to limit these emissions. Among these, an extremely lean combustion has a large potential to simultaneously reduce the NOx raw emissions and the fuel consumption of SI ICEs. Engines with pre-chamber ignition system are promising solutions for realizing a high air-fuel ratio which is both ignitable and with an adequate combustion speed. In this work, the combustion characteristics of an active pre-chamber system are experimentally investigated using a single-cylinder research engine. The engine under exam is a large bore heavy-duty unit with an active pre-chamber fuelled with compressed natural gas.

The effect of an annular, piston bowl-rim cavity on in-cylinder and engine-out soot emissions is measured in a heavy-duty, optically accessible, single-cylinder diesel engine using in-cylinder soot diagnostics and exhaust smoke emission measurements. The baseline piston configuration consists of a right-cylindrical bowl, while the cavity-piston configuration features an additional annular cavity that is located below the piston bowl-rim and connected to the main-combustion chamber through a thin annular passage, accounting for a 3% increase in the clearance volume, resulting in a reduction in geometric compression ratio (CR) from 11.22 to 10.91. Experiments using the cavity-piston configuration showed a significant reduction of engine-out smoke ranging from 20-60% over a range of engine loads.

Methanol is not a fuel typically used in compression ignition engines due to the high resistance to auto-ignition. However, conventional diesel combustion and PPC offer high engine efficiency along with low HC and CO emissions, albeit with the trade-off of increased NOx and PM emissions. This trade-off balance is mitigated in the case of methanol and other alcohol fuels, as they bring oxygen in the combustion chamber. Thus methanol compression ignition holds the potential for a clean and effective alternative fuel proposition. Most existing research on methanol is on SI engines and very little exists in the literature regarding methanol auto-ignition engine concepts. In this study, the spray characteristics of methanol inside the optically accessible cylinder of a DI-HD engine are investigated. The liquid penetration length at various injection timings is documented, ranging from typical PPC range down to conventional diesel combustion.

This study investigates particulate matter (PM) and regulated emissions from renewable rapeseed oil methyl ester (RME) biodiesel in pure and blended forms and contrasts that to conventional diesel fuel. Environmental and health concerns are the major motivation for combustion engines research, especially finding sustainable alternatives to fossil fuels and reducing diesel PM emissions. Fatty acid methyl esters (FAME), including RME, are renewable fuels commonly used from low level blends with diesel to full substitution. They strongly reduce the net carbon dioxide emissions. It is largely unknown how the emissions and characteristics of PM get altered by the combined effect of adding biodiesel to diesel and implementing modern engine concepts that reduce nitrogen oxides (NOx) emissions by exhaust gas recirculation (EGR).

In partially premixed combustion engines high octane number fuels are injected into the cylinder during the late part of the compression cycle, giving the fuel and oxidizer enough time to mix into a desirable stratified mixture. If ignited by auto-ignition such a gas composition can react in a combustion mode dominated by ignition wave propagation. 3D-CFD modeling of such a combustion mode is challenging as the rate of fuel consumption can be dependent on both mixing history and turbulence acting on the reaction wave. This paper presents a large eddy simulation (LES) study of the effects of stratification in scalar concentration (enthalpy and reactant mass fraction) due to large scale turbulence on the propagation of reaction waves in PPC combustion engines. The studied case is a closed cycle simulation of a single cylinder of a Scania D13 engine running PRF81 (81% iso-octane and 19% n-heptane).

Partially premixed combustion (PPC) is one of several advanced combustion concepts for the conventional diesel engine. PPC uses a separation between end of fuel injection and start of combustion, also called ignition dwell, to increase the mixing of fuel and oxidizer. This has been shown to be beneficial for simultaneously reducing harmful emissions and fuel consumption. The ignition dwell can be increased by means of exhaust gas recirculation or lower intake temperature. However, the most effective means is to use a fuel with high research octane number (RON). Methanol has a RON of 109 and a recent study found that methanol can be used effectively in PPC mode, with multiple injections, to yield high brake efficiency. However, the early start of injection (SOI) timings in this study were noted as a potential issue due to increased combustion sensitivity. Therefore, the present study attempts to quantify the changes in engine performance for different injection strategies.

A large number of measurement techniques have been developed or adapted from other fields to measure various parameters of engine particulates. With the strict limits given by regulations on pollutant emissions, many advanced combustion strategies have been developed towards cleaner combustion. Exhaust gas recirculation (EGR) is widely applied to suppress nitrogen oxide (NOx) and reduce soot emissions. On the other hand, gasoline starts to be utilized in compression ignition engines due to great potential in soot reduction and high engine efficiency. New engine trends raise the need for good sensitivity and suitable accuracy of the PM measurement techniques to detect particulates with smaller size and low particulate mass emissions. In this work, we present a comparison between different measurement techniques for particulate matter (PM) emissions in a compression ignition engine running on gasoline fuel. A wide-range of EGR was used with lambda varied from 3 down to 1.

Partially premixed combustion (PPC) with gasoline fuels is a new promising combustion concept for future internal combustion engines. However, many researchers have argued the capabilities of research octane number (RON) and Motor Octane Number (MON) to describe the autoignition behaviour of gasoline fuels in advanced combustion concepts like PPC. The objective of this study is to propose a new method, called PPC number, to characterize the auto ignition quality of gasoline fuels in a light-duty direct injected compression ignition engine under PPC conditions. The experimental investigations were performed on a 4-cylinder Volvo D4 2 litre engine. The ignition delay which was defined as the crank angle degrees between the start of injection (SOI) and start of combustion (SOC) was used to represent the auto ignition quality of a fuel.

NOx pollution from diesel engines has been stated as causing over 10 000 pre-mature deaths annually and predictions are showing that this level will increase [1]. In order to decrease this growing global problem, exhaust after-treatment systems for diesel engines have to be improved, this is especially so for vehicles carrying freight as their use of diesel engines is expected to carry on into the future [2]. The most common way to reduce diesel engine NOx out emissions is to use SCR. SCR operates by injecting aqueous Urea solution, 32.5% by volume (AUS-32), that evaporates prior the catalytic surface of the SCR-catalyst. Due to a catalytic reaction within the catalyst, NOx is converted nominally into Nitrogen and Water. Currently, the evaporative process is enhanced by aggressive mixer plates and long flow paths.

Partially premixed combustion (PPC) is an advanced combustion strategy that has been proposed to provide higher efficiency and lower emissions than conventional compression ignition, as well as greater controllability than homogeneous charge compression ignition (HCCI). Stratification of the fuel-air mixture is the key to achieving these benefits. The injection strategy, injector-piston geometry design and fuel properties are factors commonly manipulated to adjust the stratification level. In the authors’ previous research, the effects of injection strategy and fuel properties on the stratification formation process were investigated. The results revealed that, for a direct-injection compression ignition engine, by sweeping the injection timing from −180° aTDC (after top dead center) to −20° aTDC, the sweep could be divided into three different regimes: an HCCI regime, a Transition regime and a PPC regime, based on the changing of mixture stratification conditions.

In order to meet the requirements in the stringent emission regulations, more and more research work has been focused on homogeneous charge compression ignition (HCCI) and partially premixed combustion (PPC) or partially premixed compression ignition (PCCI) as they have the potential to produce low NOx and soot emissions without adverse effects on engine efficiency. The mixture formation and charge stratification influence the combustion behavior and emissions for PPC/PCCI, significantly. An ultra-high speed burst-mode laser is used to capture the mixture formation process from the start of injection until several CADs after the start of combustion in a single cycle. To the authors’ best knowledge, this is the first time that such a high temporal resolution, i.e. 0.2 CAD, PLIF could be accomplished for imaging of the in-cylinder mixing process. The capability of resolving single cycles allows for the influence of cycle-to-cycle variations to be eliminated.

The influence of the ignition quality of diesel-and gasoline-like fuels on the lift-off length of the jet were investigated in an optical heavy duty engine. The engine was operated at a load of 22 bar IMEPg and 1200 rpm. A production type injector with standard holes were used. The lift-off length was recorded with high speed video Different injection pressures and inlet temperatures were used to affect conditions that consequently affect the lift-off length. No matter which fuel used nor injection pressure or inlet temperature, all lift-off lengths showed equal or close to equal lift-off length when stabilized. The higher octane fuel had a longer ignition delay and therefore the fuel penetrate the combustion chamber before auto ignition. This gave a longer lift-off length at the initial stage of combustion before reaching the same stabilized lift-off length. These results indicate that the hot combustion gases are a dominant factor to the lift-off length.

The concept of Partially Premixed Combustion (PPC) in internal combustion engines has shown to yield high gross indicated efficiencies, but at the expense of gas exchange efficiencies. Most of the experimental research on partially premixed combustion has been conducted on compression ignition engines designed to operate on diesel fuel and relatively high exhaust temperatures. The partially premixed combustion concept on the other hand relies on dilution with high exhaust gas recirculation (EGR) rates to slow down the combustion which results in low exhaust temperatures, but also high mass flows over cylinder, valves, ports and manifolds. A careful design of the gas exchange system, EGR arrangement and heat exchangers is therefore of utter importance. Experiments were performed on a heavy-duty, compression ignition engine using a fuel consisting of 80 volume % 95 RON service station gasoline and 20 volume % n-heptane.

Our previous research investigated the sensitivity of combustion phasing to intake temperature and injection timing during the transition from homogeneous charge compression ignition (HCCI) to partially premixed combustion (PPC) fuelled with generic gasoline. The results directed particular attention to the relationship between intake temperature and combustion phasing which reflected the changing of stratification level with the injection timing. To confirm its applicability with the use of different fuels, and to investigate the effect of fuel properties on stratification formation, primary reference fuels (PRF) were tested using the same method: a start of injection sweep from -180° to -20° after top dead center with constant combustion phasing by tuning the intake temperature. The present results are further developed compared with those of our previous work, which were based on generic gasoline.

Humid air motor (HAM) is an engine operated with humidified inlet charge. System simulations study on HAM showed the waste heat recovery potential over a conventional system. An HAM setup was constructed, to comprehend the potential benefits in real-time, the HAM setup was built around a 13-litre six cylinder Volvo diesel engine. The HAM engine process is explained in detail in this paper. Emission analysis is also performed for all three modes of operation. The experiments were carried out at part load operating point of the engine to understand the effects of humidified charge on combustion, efficiency, and emissions. Experiments were conducted without EGR, with EGR, and with humidified inlet charge. These three modes of operation provided the potential benefits of each system. Exhaust heat was used for partial humidification process. Results show that HAM operation, without compromising on efficiency, reduces NOx and soot significantly over the engine operated without EGR.

The engine concept partially premixed combustion (PPC) has proved higher gross indicated efficiency compared to conventional diesel combustion engines. The relatively simple implementation of the concept is an advantage, however, high gas exchange losses has made its use challenging in multi-cylinder heavy duty engines. With high rates of exhaust gas recirculation (EGR) to dilute the charge and hence limit the combustion rate, the resulting exhaust temperatures are low. The selected boost system must therefore be efficient which could lead to large, complex and costly solutions. In the presented work experiments and modelling were combined to evaluate different turbocharger configurations for the PPC concept. Experiments were performed on a multi-cylinder engine. The engine was modified to incorporate long route EGR and a single-stage turbocharger, however, with compressed air from the building being optionally supplied to the compressor.

In this paper, a parametric analysis on the main engine calibration parameters applied on gasoline Partially Premixed Combustion (PPC) is performed. Theoretically, the PPC concept permits to improve both the engine efficiencies and the NOx-soot trade-off simultaneously compared to the conventional diesel combustion. This work is based on the design of experiments (DoE), statistical approach, and investigates on the engine calibration parameters that might affect the efficiencies and the emissions of a gasoline PPC. The full factorial DoE analysis based on three levels and three factors (33 factorial design) is performed at three engine operating conditions of the Worldwide harmonized Light vehicles Test Cycles (WLTC). The pilot quantity (Qpil), the crank angle position when 50% of the total heat is released (CA50), and the exhaust gas recirculation (EGR) factors are considered. The goal is to identify an engine calibration with high efficiency and low emissions.

In a previous study, in order to investigate the effect of charge stratification on combustion behavior such as combustion efficiency and combustion phasing which also largely affects the emissions, an experiment was conducted in a heavy-duty compression ignition (CI) metal engine. The engine behavior and emission characteristics were studied in the transition from HCCI mode to PPC mode by varying the start of injection (SOI) timing. To gain more detailed information of the mixing process, in-cylinder laser diagnostic measurements, namely fuel-tracer planar laser induced fluorescence (PLIF) imaging, were conducted in an optical version of the heavy-duty CI engine mentioned above. To the authors’ best knowledge, this is the first time to perform fuel-tracer PLIF measurements in an optical engine with a close to production bowl in piston combustion chamber, under transition conditions from HCCI to PPC mode.

Diesel engine manufacturers strive towards further efficiency improvements. Thus, reducing in-cylinder heat losses is becoming increasingly important. Understanding how location, thermal insulation, and engine operating conditions affect the heat transfer to the combustion chamber walls is fundamental for the future reduction of in-cylinder heat losses. This study investigates the effect of a 1mm-thick plasma-sprayed yttria-stabilized zirconia (YSZ) coating on a piston. Such a coated piston and a similar steel piston are compared to each other based on experimental data for the heat release, the heat transfer rate to the oil in the piston cooling gallery, the local instantaneous surface temperature, and the local instantaneous surface heat flux. The surface temperature was measured for different crank angle positions using phosphor thermometry.

In this paper, a control-oriented soot model was developed for real-time soot prediction and combustion condition optimization in a gasoline Partially Premixed Combustion (PPC) Engine. PPC is a promising combustion concept that achieves high efficiency, low soot and NOx emissions simultaneously. However, soot emissions were found to be significantly increased with high EGR and pilot injection, therefore a predictive soot model is needed for PPC engine control. The sensitivity of soot emissions to injection events and late-cycle heat release was investigated on a multi-cylinder heavy duty gasoline PPC engine, which indicated main impact factors during soot formation and oxidation processes. The Hiroyasu empirical model was modified according to the sensitivity results, which indicated main influences during soot formation and oxidation processes. By introducing additional compensation factors, this model can be used to predict soot emissions under pilot injection.