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Hydrogen as homogeneous charge compression ignition engine fuel

Hydrogen has been proposed as a possible fuel for automotive applications. This paper reports an experimental investigation of hydrogen as HCCI engine fuel. The aim of the experimental study is to investigate the possibility to run an HCCI engine on an extremely fast burning fuel such as hydrogen as well as to study the efficiency, the combustion phasing and the formation of emissions. The experiments were conducted on a single-cylinder research engine with a displacement volume of 1.6 litres and pancake combustion chamber geometry. Variation of lambda, engine speed, compression ratio and intake temperature were parts of the experimental setting. The engine was operated in Homogenous Charge Compression Ignition (HCCI) mode and as comparison also in Spark Ignition (Sl) mode. Hydrogen was found to be a possible fuel for an HCCI engine. The heat release rate was extremely high and the interval of possible start of combustion crank angles was found to be narrow. The high rate of heat release limited the operating range to lean (λ>3) conditions. On the other hand operation on extremely lean mixtures (X=6) was found possible. The possible operating range was investigated when intake gas temperature was used for control and also this control interval was found to be narrow, especially when richer cases were run. The maximum load in HCCI mode was an IMEPn of 3.5 bar which is about half of the load possible in Sl mode and about half the maximum load in HCCI mode with other fuels. For the loads where HCCI operation could be conducted indicated thermal efficiency for HCCI was superior to that of SI. NOx emissions were, as expected, found to decrease when lambda was increased and the levels were very low in HCCI mode. High levels of hydrogen were found in the exhaust with HCCI. When the engine was operated on low lambdas (i.e. λ=3) emissions of carbon monoxide and hydrocarbons were detected, probably originating from evaporated and partially oxidized lubrication oil.

Measurement of Knock and Ion Current in a Spark Ignition Engine with and without NO Addition to the Intake Air

Several studies have shown that NO has a strong influence on engine knock. This paper reports an experimental study that addresses the connection between SI engine knock and the level of nitric oxide, NO, in the intake manifold gas under various conditions of engine operation. Some theories explain the second ion-current peak as thermal ionisation of NO. Both temperature and NO concentration is of importance. By advancing the ignition angle the NO concentration can be increased, but the temperature is also increased. Addition of NO in the inlet manifold increases the NO concentration but has less effect on the temperature. SI engine experiments were conducted over a number of different ignition timings, air/fuel ratios, engine speeds and intake manifold pressures. The NO level in the intake manifold was altered from 100 to 1600 ppm, increasing the amount by doubling. The study confirms that there is an increasing tendency of early knock when the NO amount increases. A slight increase in the second ion-current peak could be seen with addition of NO in the inlet manifold, especially with early ignition timing. This increase in peak amplitude may be a result of heavy knock, due to the addition of NO. Advancing the ignition angle 2 crank angle degrees has a stronger influence on the second ion-current peak than addition of 1600 ppm NO in the inlet manifold.

In-Cycle Closed Loop Control Of The Fuel Injection On A 1-Cylinder Heavy Duty Ci-Engine

The focus of this article is on implementation of real time combustion control by using an FPGA. The feedback used for the controller is the heat release. Due to the desire to avoid using division on the FPGA an alternative way of calculating the polytropic exponent is investigated. When this method is compared against using a constant exponent it shows less fluctuations in regards to cycle to cycle variations when calculating the heat release. A dual injection strategy is used and real time control is implemented on the second fuel injection. The calculated heat release is continuously compared with a reference and then the difference is converted to a duration correction of the filet injection. This is done by a proportional controller which is initiated after the start of the second injection. By adding a perturbation on the first fuel injection the controller is shown to compensate during the second and thereby decreasing the cycle to cycle variations. (Less)

Zero-dimensional modeling of NOx formation with least squares interpolation

Physical models of NO x formation are becoming more and more interesting in the area of combustion feedback control. The fact that cylinder pressure sensors are made available on the market enables fast and accurate calculations of heat release, which is an essential part of every physical NO x formation model. This article describes such a zero-dimensional model for a diesel engine using crank angle–resolved cylinder pressure to determine heat release. The model also incorporates the thermal effect of exhaust gas recirculation that is proven to have a major effect on NO x formation rates. The reaction mechanisms used to describe NO x formation rates are given by the well-known Zeldovich mechanism. The model output results given in this article show an average deviation of about 12.0% from acquired measured NO x data. The least squares interpolation approach indicates a negligible difference from the original model with an average deviation of 1.2% in 25 measurement points.

Reformed Methanol Gas as Homogeneous Charge Compression Ignition Engine Fuel

Hydrogen has been proposed as a possible fuel for automotive applications. Methanol is one of the most efficient ways to store and handle hydrogen. By catalytic reformation it is possible to convert methanol into hydrogen and carbon monoxide. This paper reports an experimental investigation of Reformed Methanol Gas as Homogeneous Charge Compression Ignition (HCCI) engine fuel. The aim of the experimental study is to investigate the possibility to run an HCCI engine on a mixture of hydrogen and carbon monoxide, to study the combustion phasing, the efficiency and the formation of emissions. Reformed Methanol Gas (RMG) was found to be a possible fuel for an HCCI engine. The heat release rate was lower than with pure hydrogen but still high compared to other fuels. The interval of possible start of combustion crank angles was found to be narrow but wider than for hydrogen. The high rate of heat release limited the operating range to lean (glmg3) cases as with hydrogen. On the other hand, operation on extremely lean mixtures (glme6) was possible. The operating range was investigated using intake air temperature for control and also this control interval was found to be narrow but more extensive than for pure hydrogen, especially when richer cases were run. The maximal load in HCCI mode was a net Indicated Mean Effective Pressure (IMEPn) of 3.5 bar for RMG. This is the same maximum IMEPn as for hydrogen. It is about half the load possible in Spark Ignition (SI) mode and about half the maximal load in HCCI mode with other fuels. For the loads where HCCI operation was possible, indicated thermal efficiency for HCCI was superior to that of SI operation. The indicated overall efficiency of the engine-reformer system is as high for SI as for HCCI operation when RMG is used as fuel. NOx emissions were, as expected, found to decrease when the equivalence ratio was lowered. High levels of carbon monoxide were found in the exhaust. Emissions of hydrocarbons were detected, probably originating from evaporated and partially oxidized lubrication oil. (Less)

A Study on In-Cycle Control of NOx Using Injection Strategy with a Fast Cylinder Pressure Based Emission Model as Feedback

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. Studies of injection strategies show that one of the feasible approaches, using a solenoid injector to control NOx, is a split-main injection based strategy. Results suggest that it is hard to control the NOx in a satisfactory manner. Really low injection pressures and long injection durations had to be applied to achieve control of the NOx formation. This also implies inherently high smoke emissions. The strategy allows NOx reduction but measurement and emission estimation results indicate that the delay between fuel injection and the maximum NOx concentration is too long. The NOx target value defined could never be satisfied using the feedback-based split-main injection strategy. Prediction-based feedback will be necessary to improve the control. (Less)

Turbocharger Speed Estimation via Vibration Analysis

Due to demanding legislation on exhaust emissions for internal combustion engines and increasing fuel prices, automotive manufacturers have focused their efforts on optimizing turbocharging systems ...

A Fast Crank Angle Resolved Zero-Dimensional NOx Model Implemented on a Field-Programmable Gate Array

In the automotive industry, the piezo-based in-cylinder pressure sensor is getting commercialized and used in production vehicles. For example, the pressure sensor offers the opportunity to design algorithms for estimation of engine emissions, such as soot and NO, during a combustion cycle. In this paper a zero-dimensional NO model for a diesel engine is implemented that will be used in real time. The model is based on the thermal NO formation and the Zeldovich mechanism using two non-geometrical zones: burned and unburned zone. The influence of EGR on combustion temperature was modeled using a well-known thermodynamic identity where specific heat at constant pressure is included. Specific heat will vary with temperature and the gas composition. The model was implemented in LabVIEW using tools specific for an FPGA (Field-Programmable Gate Array). In order to simplify and implement the model, least-squares-criterion-based polynomial approximations are used that enables the utilization of fast algorithms as well as sub-routines (sub-VIs). The sub-routines can be used to save space on the Field Programmable Gate Array (FPGA) and thus minimizing the risk of potential issues regarding overmapping of the hardware. In this case the interpolating functions are polynomials that only consume addition and multiplication operations. This is suited for the objective in mind due to the fact that the model tailored for an FPGA cannot, in a sufficient manner, handle highly complex calculations nor divisions. The time results obtained during the execution of the model indicates that it is possible to update the NO, at a given temporal state, well below the time corresponding to a crank angle degree. The FPGA NO model was tested against measurement data collected from a Scania engine. The time needed to execute an iteration of the model was approximately 3 μs. (Less)

Torque Estimation Based Virtual Crank Angle Sensor

In engine management systems many calculations and actuator actions are performed in the crank angle domain. Most of these actions and calculations benefit from an improved accuracy of the crank an ...

Pressure Ratio Influence on Exhaust Valve Flow Coefficients

In one dimensional engine simulation software, flow losses over complex geometries such as valves and ports are described using flow coefficients. It is generally assumed that the pressure ratio ov ...