Modern Common-rail Diesel Engine Research Articles

Performance and Emission Analysis of Common Rail Diesel Engine with Microalgae Biodiesel

Modern common rail diesel engines are normally optimized with commercial diesel. As a result, the engine control unit’s calibration is established to achieve the best compromise between performances and exhaust pollutants. Biodiesel has a faster combustion rate and higher combustion chamber temperature than commercial diesel, which necessitates the injection of higher fuel volumes to compensate for the lower calorific value of biodiesel compared to regular diesel. This study showed that by adjusting the mapping of the engine control unit according to the fuel utilised, it is possible to improve the emissions and performance of a common rail diesel engine running on pure Botryococcus braunii algae oil biodiesel or a blend of biodiesel and commercial diesel.

Thermophysical properties of rapeseed oil methyl esters (RME) at high pressures and various temperatures evaluated by ultrasonic methods

Investigation of the high-pressure thermophysical properties of biofuels, e.g., bulk modulus, surface tension, and viscosity is of paramount importance in fuel injection systems in diesel engines. Another crucial and dangerous phenomenon that may occur in biofuels at high pressures is phase transition (solidification), which can drastically increase the viscosity of the biofuel. This effect may hamper proper operation of the engine, especially under cold-start conditions. Unfortunately, the availability of high-pressure thermophysical properties of biofuels is still limited. The goal of this paper is to investigate the impact of high pressures on thermophysical properties of biofuels on the example of rapeseed fatty acid methyl esters (RME) in a wide range of pressures (0.1to250MPa) and temperatures (5to20°C). To this end we employed innovative ultrasonic techniques, i.e., the Bleustein-Gulyaev surface acoustic waves for measuring RME viscosity, and ultrasonic bulk compressional waves for measuring sound velocity in RME and consequently evaluating RME thermophysical parameters, e.g., bulk modulus and surface tension. The viscosity of the measured RME displayed an abrupt increase at pressures: 260 MPa (t=20°C), 230 MPa (t=15°C), 190 MPa (t=10°C), and 130 MPa (t=5°C). Evidently it was a signature of the phase transition (solidification) occurring in the RME. The discovered high viscosity high-pressure phase in RME can be very detrimental for operation of modern common rail Diesel engines. Therefore, the results of research presented in this paper should be interesting for engineers and designers working with modern common rail Diesel engines using biofuels.

Effect of atmospheric aging on volatility and reactive oxygen species of biodiesel exhaust nano-particles

Abstract. In the prospect of limited energy resources and climate change, effects of alternative biofuels on primary emissions are being extensively studied. Our two recent studies have shown that biodiesel fuel composition has a significant impact on primary particulate matter emissions. It was also shown that particulate matter caused by biodiesels was substantially different from the emissions due to petroleum diesel. Emissions appeared to have higher oxidative potential with the increase in oxygen content and decrease of carbon chain length and unsaturation levels of fuel molecules. Overall, both studies concluded that chemical composition of biodiesel is more important than its physical properties in controlling exhaust particle emissions. This suggests that the atmospheric aging processes, including secondary organic aerosol formation, of emissions from different fuels will be different as well. In this study, measurements were conducted on a modern common-rail diesel engine. To get more information on realistic properties of tested biodiesel particulate matter once they are released into the atmosphere, particulate matter was exposed to atmospheric oxidants, ozone and ultra-violet light; and the change in their properties was monitored for different biodiesel blends. Upon the exposure to oxidative agents, the chemical composition of the exhaust changes. It triggers the cascade of photochemical reactions resulting in the partitioning of semi-volatile compounds between the gas and particulate phase. In most of the cases, aging lead to the increase in volatility and oxidative potential, and the increment of change was mainly dependent on the chemical composition of fuels as the leading cause for the amount and the type of semi-volatile compounds present in the exhaust.

Direct injection of neat n-butanol for enabling clean low temperature combustion in a modern diesel engine

This study investigates the effects of neat n-butanol replacing conventional diesel fuels to enable clean combustion on a modern common-rail diesel engine. Systematic engine experiments are conducted to examine the combustion characteristics and exhaust emissions in correlation to n-butanol’s relatively high oxygen content and high volatility but low ignitability, and control strategies are thereafter developed for enabling clean and efficient combustion of neat n-butanol. Compared to its diesel counterpart, the single-shot injection of neat n-butanol offers substantially reduced NOx emissions without the use of EGR and near-zero soot emissions, but the applicable injection timing window is narrower for n-butanol limited by high maximum rates of pressure rise and/or unstable combustion. EGR is effective to reduce the combustion roughness, but it further narrows the applicable injection timing window and deteriorates the HC and CO emissions. A control strategy that deploys multi-shot injections combined with moderate use of EGR is developed and applied to improve the combustion controllability and exhaust emissions while minimizing the penalties in the engine efficiency.

Influence of fuel molecular structure on the volatility and oxidative potential of biodiesel particulate matter.

We have studied the effect of chemical composition of biodiesel fuel on the physical (volatility) and chemical (reactive oxygenated species concentration) properties of nano particles emitted from a modern common-rail diesel engine. Particle emissions from the combustion of four biodiesels with controlled chemical compositions and different varying unsaturation degrees and carbon-chain lengths, together with a commercial diesel, were tested and compared in terms of volatility of particles and the amount of reactive oxygenated species carried by particles. Different blends of biodiesel and petro diesel were tested at several engine loads and speeds. We have observed that more saturated fuels with shorter carbon chain lengths result in lower particle mass but produce particles that are more volatile and also have higher levels of Reactive Oxygen Species. This highlights the importance of taking into account metrics that are relevant from the health effects point of view when assessing emissions from new fuel types.

Inter-cycle variability of in-cylinder pressure parameters in an ethanol fumigated common rail diesel engine

The effects of ethanol fumigation on the inter-cycle variability of key in-cylinder pressure parameters in a modern common rail diesel engine have been investigated. Specifically, maximum rate of pressure rise, peak pressure, peak pressure timing and ignition delay were investigated. A new methodology for investigating the start of combustion was also proposed and demonstrated—which is particularly useful with noisy in-cylinder pressure data as it can have a significant effect on the calculation of an accurate net rate of heat release indicator diagram. Inter-cycle variability has been traditionally investigated using the coefficient of variation. However, deeper insight into engine operation is given by presenting the results as kernel density estimates; hence, allowing investigation of otherwise unnoticed phenomena, including: multi-modal and skewed behaviour. This study has found that operation of a common rail diesel engine with high ethanol substitutions (>20% at full load, >30% at three quarter load) results in a significant reduction in ignition delay. Further, this study also concluded that if the engine is operated with absolute air to fuel ratios (mole basis) less than 15, the inter-cycle variability is substantially increased compared to normal operation.

Effect of soot accumulation in a diesel particle filter on the combustion process and gaseous emissions

Particulate filters are massively used in new diesel vehicles to reduce particulate emissions below the regulation limits. The setting of filters in the exhaust lines imposes various changes in the engine working conditions, including increased back-pressure, resulting in some fuel penalty. In this work, the filter loading process was investigated in a modern common-rail diesel engine equipped with diesel oxidation catalyst and diesel particulate filter. The engine was fuelled with EN-590 diesel fuel and run in a highly emissive operating mode selected among those reproducing the New European Driving Cycle. During the test the intake/exhaust conditions, intake charge, injection and combustion timing, fuel consumption and regulated emissions were measured. It was observed that the EGR (exhaust gas recirculation) ratio decreased from 30% down to 21%, shifting the combustion process away from its design parameters. In consequence, nitrogen oxides emissions increased around 60% along the test, compromising the objectives of the emission regulations. A 4% increase in fuel consumption throughout the test was measured, this value being higher than that expected from previous literature. An energy balance revealed that such penalty was caused by increased pumping losses and, especially, by higher energy losses via exhaust gas temperature and engine coolant.

Stock and Optimized Performance and Emissions with 5 and 20% Soy Biodiesel Blends in a Modern Common Rail Turbo-Diesel Engine

Stock engine design and decision making target optimal performance with conventional diesel fuel, leading to suboptimal results for biodiesel. The main result of this study is the determination of the appropriate engine decision making for the air/fuel ratio (AFR), exhaust gas recirculation (EGR) fraction, injection (rail) pressure, and start of main fuel injection (SOI) in a modern common rail diesel engine using variable-geometry turbo charging and operating with 5% (B5) and 20% (B20) soy-based biodiesel fuel mixtures to minimize brake-specific fuel consumption (BSFC) while adhering to strict combustion noise, NOx and PM emission constraints. In so doing, this effort determined to what extent the optimal AFR, EGR fraction, rail pressure, and SOI settings can (1) overcome the well-known “biodiesel−NOx effect” and (2) mitigate the impact of lower biodiesel energy density on BSFC for B5 and B20 biodiesel blends. Study findings indicate that lower AFR, higher EGR fraction, and earlier start of main injectio...

A Phenomenological Mean Value Soot Model for Transient Engine Operation

A means of characterizing the raw soot emissions from modern common-rail diesel engines is required so that their control and the regeneration of an associated particulate filter can be optimized, though no suitable sensor currently exists. Thus, under the framework of a FVV research project, a fast soot model to calculate the raw soot emissions from a common-rail diesel engine operating under both steady state and transient operating conditions was developed and validated at the Aerothermochemistry and Combustion Systems Laboratory (LAV) at the ETH Zurich.

Combustion Study of a Common Rail Diesel Engine Optimized to be Fueled with Biodiesel

The automobile market is, nowadays, characterized by a growing demand for cars equipped with diesel engines. This is because these offer smaller fuel consumption and better engine performance. A modern common rail turbocharged diesel engine provides performance equal to a gasoline engine, with same displacement, not turbo-charged but with a higher torque at lower engine speeds and with smaller fuel consumption. The methyl esters of vegetable oils, known as biodiesel, are receiving increasing interest because of their low environmental impact and their potential as an alternative fuel for diesel engines as they would not require any significant modification of existing engines. The modern common rail (CR) diesel engines are normally optimized for commercial diesel fuel. Consequently, the Electronic Control Unit (ECU) calibrations are defined to offer the best compromise between performance and emissions. If the engine is fuelled with an alternative fuel with different characteristics (net heating value, stoichiometric air fuel ratio (a/f), density, viscosity, etc.), it is clear that the calibration must be modified. In past experiments the authors have demonstrated that it is possible to optimize emissions and performances of a light duty CR diesel engine fueled with a vegetable derived fuel (rapeseed methyl ester) pure or blended with commercial diesel fuel, changing ECU parameters. This paper will show a detailed analysis of combustion in a modern diesel engine fueled with biodiesel and in particular some of the influences on engine parameters will be analyzed in order to demonstrate how an optimization strategy of ECU parameters could be applied to a diesel engine, when it is fueled with different fuels, with different physical/chemical characteristics.

Model-based fault detection and diagnosis with special input excitation applied to a modern diesel engine

Due to the rising complexity of many technical processes modern diagnosis systems have to supervise a multitude of hydraulic, mechanical, electromechanical and mechatronic components. Therefore model-based methods of fault-detection and diagnosis have been developed. These methods use mathematical process models to relate data of several measurable variables. Thus the diagnosis quality depends on the available sensor data. In order to obtain additional information with the given sensor configuration special input excitation signals can be used. This paper will describe a method to locate faults in multivariable systems using such input excitation and its application to the intake air system of a modern common rail Diesel engine. The presented method uses the knowledge of fault effects on the measured output, when the inputs are successively excited quasi-stationary, to determine the location of the fault. It has been applied successfully to differentiate air mass sensor faults from other process faults.

On the generation of aerosol for diesel particulate filtration studies

Abstract The three different ways for the generation of carbon particulate aerosols were considered to simulate the exhaust gases of the latest-generation Common-Rail Diesel engines for vehicle application: a small Diesel engine for electric power generation modules, an acetylene burner, and an ad hoc designed ‘fluidised bed’ pilot plant. The final goal of this work is to develop a simple and reliable apparatus to improve the knowledge of the filtration mechanisms for different particulate traps, avoiding the need to build-up large and expensive Diesel engine benches. The particles shape, their composition and size distribution have been assessed to compare the aerosols generated by the three pilot plants with those typical of the modern Common-Rail Diesel engines for passenger cars. Ceramic foam filters are finally employed as a common reference to check whether the filtration results obtained with the particles produced by such pilot plants are representative of those determined with their large-scale counterpart or not.

Fired and non-fired engine: A comparative study of crankcase emission on dynamometer test rigs

In engine development, the design of the crankcase ventilation system can only begin at a relatively late stage, due to the lack of engines for fired operation. However, as engines for non-fired operation are commonly available prior to that, tests on these engines may enable early design studies of crankcase ventilation. This article presents comparative tests with a modern 4-cylinder common rail diesel engine.