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Gas engines (fuelled with CNG, LNG or Biogas) for generation of power and heat are, to this date, taking up larger shares of the market with respect to diesel engines. In order to meet the limit imposed by the TA-Luft regulations on stationary engines, lean combustion represents a viable solution for achieving lower emissions as well as efficiency levels comparable with diesel engines. Leaner mixtures however affect the combustion stability as the flame propagation velocity and consequently heat release rate are slowed down. As a strategy to deliver higher ignition energy, an active pre-chamber may be used. This work focuses on assessing the performance of a pre-chamber combustion configuration in a stationary heavy-duty engine for power generation, operating at different loads, air-to-fuel ratios and spark timings.

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).

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.

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.

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.

In order to reduce nitrogen oxides (NOx) and soot emissions while maintaining high thermal efficiency, more advanced combustion concepts have been developed over the years, such as Homogeneous Charge Compression Ignition (HCCI) and Partially Premixed Combustion (PPC), as possible combustion processes in commercial engines. Compared to HCCI, PPC has advantages of lower unburned hydrocarbon (UHC) and carbon monoxide (CO) emissions; however, due to increased fuel stratifications, soot emissions can be a challenge when adding Exhaust-Gas Recirculation (EGR) gas. The current work presents particle size distribution measurements performed from HCCI-like combustion with very early (120 CAD BTDC) to PPC combustion with late injection timing (11 CAD BTDC) at two intake oxygen rates, 21% and 15% respectively. Particle size distributions were measured using a differential mobility spectrometer DMS500.

This article presents a study related to application of pre-chamber ignition system in heavy duty natural gas engine which, as previously shown by the authors, can extend the limit of fuel-lean combustion and hence improve fuel efficiency and reduce emissions. A previous study about the effect of pre-chamber volume and nozzle diameter on a single cylinder 2 liter truck-size engine resulted in recommendations for optimal pre-chamber geometry settings. The current study is to determine the dependency of those settings on the engine size. For this study, experiments are performed on a single cylinder 9 liter large bore marine engine with similar pre-chamber geometry and a test matrix of similar and scaled pre-chamber volume and nozzle diameter settings. The effect of these variations on main chamber ignition and the following combustion is studied to understand the scalability aspects of pre-chamber ignition. Indicated efficiency and engine-out emission data is also presented.

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.

Partially premixed combustion (PPC) is a promising way to achieve high efficiency and low engine-out emissions simultaneously in a heavy-duty engine. Compared to Homogeneous Charge Compression Ignition (HCCI), it can be controlled by injection events and much lower HC and CO emissions can be achieved. This work focuses on the transition from HCCI to PPC and combustion and emissions characteristics during the process are investigated. Injection strategies, EGR and boost pressure were the main parameters used to present the corresponding effect during the transition.

The effect of pre-chamber volume and nozzle diameter on performance of pre-chamber ignition device in a heavy duty natural gas engine has previously been studied by the authors. From the analysis of recorded pre- and main chamber pressure traces, it was observed that a pre-chamber with a larger volume reduced flame development angle and combustion duration while at a given pre-chamber volume, smaller nozzle diameters provided better ignition in the main chamber. The structure of pre-chamber jet and its mixing characteristics with the main chamber charge are believed to play a vital role, and hence CFD simulations are performed to study the fluid dynamic aspects of interaction between the pre-chamber jet and main chamber charge during the period of flame development angle, i.e. before main chamber ignition. It has been observed that jets from a larger pre-chamber penetrates through the main chamber faster due to higher momentum and generates turbulence in the main chamber earlier.

It has previously been shown by the authors that the pre-chamber ignition technique operating with fuel-rich pre-chamber combustion strategy is a very effective means of extending the lean limit of combustion with excess air in heavy duty natural gas engines in order to improve indicated efficiency and reduce emissions. This article presents a study of the influence of pre-chamber volume and nozzle diameter on the resultant ignition characteristics. The two parameters varied are the ratio of pre-chamber volume to engine's clearance volume and the ratio of total area of connecting nozzle to the pre-chamber volume. Each parameter is varied in 3 steps hence forming a 3 by 3 test matrix. The experiments are performed on a single cylinder 2L engine fitted with a custom made pre-chamber capable of spark ignition, fuel injection and pressure measurement.

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.

Partially Premixed Combustion (PPC) has the potential of simultaneously providing high engine efficiency and low emissions. Previous research has shown that with proper combination of Exhaust-Gas Recirculation (EGR) and Air-Fuel equivalence ratio, it is possible to reduce engine-out emissions while still keeping the engine efficiency high. In this paper, the effect of changes in intake pressure (boost) and EGR fraction on PPC engine performance (e.g. ignition delay, burn duration, maximum pressure rise rate) and emissions (carbon monoxide (CO), unburned hydrocarbon (UHC), soot and NOX) was investigated in a single-cylinder, heavy-duty diesel engine. Swedish diesel fuel (MK1), RON 69 gasoline fuel and 99.5 vol% ethanol were tested. Fixed fueling rate and single injection strategy were employed.

Emissions and in-cylinder pressure traces are used to compare the relative importance of soot formation and soot oxidation in a heavy-duty diesel engine. The equivalence ratio at the lift-off length is estimated with an empirical correlation and an idealized model of diesel spray. No correlation is found between the equivalence ratio at lift-off and the soot emissions. This confirms that trends in soot emissions cannot be directly understood by the soot formation process. The coupling between soot emission levels and late heat release after end of injection is also studied. A regression model describing soot emissions as function of global engine parameters influencing soot oxidation is proposed. Overall, the results of this analysis indicate that soot emissions can be understood in terms of the efficiency of the oxidation process.

This article deals with application of turbulent jet ignition technique to heavy duty multi-cylinder natural gas engine for mobile application. Pre-chamber spark plugs are identified as a promising means of achieving turbulent jet ignition as they require minimal engine modification with respect to component packaging in cylinder head and the ignition system. Detailed experiments were performed with a 6 cylinder 9.4 liter turbo-charged engine equipped with multi-point gas injection system to compare performance and emissions characteristics of operation with pre-chamber and conventional spark plug. The results indicate that ignition capability is significantly enhanced as flame development angle and combustion duration are reduced by upto 30 % compared to those with conventional spark plugs at certain operating points.