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Compressed natural gas (CNG) is an attractive, alternative fuel for spark-ignited (SI), internal combustion (IC) engines due to its high octane rating, and low energy-specific CO2 emissions compared with gasoline. Directly-injected (DI) CNG in SI engines has the potential to dramatically decrease vehicles’ carbon emissions; however, optimization of DI CNG fueling systems requires a thorough understanding of the behavior of CNG jets in an engine environment. This paper therefore presents an experimental and modeling study of DI gaseous jets, using methane as a surrogate for CNG. Experiments are conducted in a non-reacting, constant volume chamber (CVC) using prototype injector hardware at conditions relevant to modern DI engines. The schlieren imaging technique is employed to investigate how the extent of methane jets is impacted by changing thermodynamic conditions in the fuel rail and chamber.

A test procedure was developed to assess the deposit-forming tendencies of gasoline/ethanol fuel blends, ranging from 0 % to 100 % ethanol (E0 to E100). The test engine was a Ford 1.8l - 4 cylinder -16 valve -natural aspirated flex fuel engine, which is used in various vehicle models, such as the European Focus and C-MAX. The test cycle, a realistic engine speed/torque profile, based on an urban driving pattern, provided good differentiation between different gasoline/ethanol fuel blends as well as between additized and non-additized fuel blends. With unadditized E85 critical deposits were found in the intake system, on the intake valves, in the combustion chamber and on the injector tips. Well known deposit control additives (DCA) used in gasoline such as PIBA (polyisobutyleneamine) and PEA (polyetheramine) were examined in E85 for deposit control effectiveness of intake valves, injectors and combustion chambers.

Due to their CO2 reduction potential and their high knock resistance gaseous fuels present a promising alternative for modern highly boosted spark ignition engines. Especially the direct injection of LPG reveals significant advantages. Previous studies have already shown the highest thermodynamic potential for the LPG direct injection concept and its advantages in comparison to external mixture formation systems. In the performed research study a comparison of different LPG fuels in direct injection mode shows that LPG fuels have better auto-ignition behavior than gasoline. A correlation between auto-ignition behavior and the calculated motor octane number could not be found. However, a significantly higher correlation of R2 = 0.88 - 0.99 for CR13 could be seen when using the methane number. One major challenge in order to implement the LPG direct injection concept is to ensure the liquid state of the fuel under all engine operating conditions.

Spark ignited engines with direct fuel injection into the combustion chamber can be started by injecting fuel into the combustion chamber of the stopped engine and igniting it afterwards with the spark plug. The explosion of the air fuel mixture initially rotates the crankshaft. The engine is started without motoring the crankshaft with a starter device. The described start procedure is called “Direct Start”. For a successful Direct Start a maximum oxygen concentration in the “Direct Start Cylinders” (the cylinders utilized initially for the Direct Start) is required, because the oxygen concentration in the start cylinders determines the maximum amount of energy, which can be exploited to move the crankshaft over the following “TDC” (Top Dead Center). After the engine stop the Direct Start Cylinder valves are closed. Therefore the oxygen concentration has to be maximized during the preceding engine shut down.

Liquefied Petroleum Gas direct injection (LPG DI) is believed to be the key enabler for the adaption of modern downsized gasoline engines to the usage of LPG, since LPG DI avoids the significant low end torque drop, which goes along with the application of conventional LPG port fuel injection systems to downsized gasoline DI engines, and provides higher combustion efficiencies. However, especially the high vapor pressure of C3 hydrocarbons can result in hot fuel handling issues as evaporation or even in reaching the supercritical state of LPG upstream or inside the high pressure pump (HPP). This is particularly critical under hot soak conditions. As a result of a rapid fuel density drop close to the supercritical point, the HPP is not able to keep the rail pressure constant and the engine stalls.

So far, the effect of injection rate shaping on the diesel combustion in small-bore DI diesel engines has not been extensively investigated, especially at high part load conditions with high EGR rates. The benefit of injection rate shaping is already verified for heavy duty engines at high load conditions with and without EGR. For this investigation, single cylinder engine investigations were conducted at the VKA / RWTH Aachen University. In order to meet the future NOx legislation limits like US-Tier2Bin5 it is crucial to reduce NOx especially at the high load points of the certification cycles, as FTP75 or US06. For the single cylinder investigations two part load points were chosen, which have relevance for the mentioned certification cycles. The experimental work focuses on different rate shapes as rectangular (Common-Rail type), ramp and boot shape at high EGR rates.

The purpose of this study is to investigate the effect of spray-bowl interaction on combustion, and pollutants formation at one specific high-load point of a single-cylinder small-bore diesel engine through computational analysis. The simulations are performed using Representative Interactive Flamelet (RIF) model with detailed chemical kinetics. Detailed chemistry-based soot model is used for the prediction of soot emissions. The simulations are performed for five different injection timings. Model-predicted cylinder pressure and exhaust emissions are validated against the measured data for all the injection timings. A new method - Two-part analysis - is then applied to investigate the spray-bowl interaction. Two-part analysis splits the volume of the combustion chamber into two, namely the piston bowl and the squish volume. Through analysis, among others the histories of soot, carbon monoxide (CO) and nitric oxide (NO ) emissions inside both volumes are shown.

A fundamental requirement for natural gas (NG) and renewable methane (e.g. bio-methane or power-to-gas methane) as automotive fuel is reliable knock resistance; to enable optimization of dedicated NG engines with high compression ratio and high turbocharger boost (which enables considerable engine downsizing factors). In order to describe the knock resistance of NG, the Methane Number (MN) has been introduced. The lowest MN which generally can be found in any NG is 65, and the vast majority of NG (~ 99.8%) is delivered with a MN above 70. The MN of bio-methane and power-to-gas methane is usually far above 80. Thus, from an automotive point of view any methane fuel should at least provide a minimum Methane Number of 70 at any point of sale. But the European draft standard describing the automotive CNG fuel quality so far proposes a minimum MN limit of 65.

Twin camshaft phasing was applied to a 1.6l 4-cylinder 16-valve DOHC engine. Both camshafts - intake and exhaust - were equipped with continuously adjustable cam phasing units. Different operating strategies were compared with regard to mechanical feasibility, thermodynamics and calibration. Attractive part load fuel economy was achieved with two different phasing strategies. With regard to full load and idle a preferred twin camshaft phasing strategy was determined. It was found favorable to shift the intake camshaft largely towards ‘advance’, and the exhaust camshaft towards ‘retard’. Maximum fuel economy improvement was 8% at 2500 rpm and 3 bar mean effective pressure. In the European drive cycle 5 % fuel economy improvement was obtained. To achieve superior performance it is mandatory to combine twin camshaft phasing with an appropriate exhaust system and optimized cam events.