Rolf Egnell

Combustion Diagnostics by Means of Multizone Heat Release Analysis and NO Calculation

In this paper a combustion diagnostic method is presented where measured pressure data is used to calculate the heat release, local temperatures and concentrations of NO and other species. This is done by a multizone model where the lambda value, i.e. 1/equivalence ratio, in each zone can be chosen arbitrarily. In homogenous charge engines lambda is given by the global air/fuel ratio. The local lambdas during initial combustion in stratified charge and diesel engines have to be estimated either as an average value or with a chosen distribution. One new zone of each local lambda is generated and the temperature, volume and species in all old zones are updated at each time step of calculation. In this paper the model is demonstrated by using pressure data from premixed and direct injected stratified charge natural gas SI engines and from a DI diesel engine. The pre-mixed data is used to validate the model as such while the ambition in the stratified charge and diesel cases has been to find the average local lambda that gives the same NOx emission as measured. The emphasis in the latter cases has been to study the influence on average local lambda of the duration of the fuel injection. Early injected fuel seems to burn at slightly leaner mixtures than later injected. (Less)

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.

Detailed Heat Release Analyses With Regard To Combustion of RME and Oxygenated Fuels in an HSDI Diesel Engine

Experiments on a modern DI Diesel engine were carried out: The engine was fuelled with standard Diesel fuel, RME and a mixture of 85% standard Diesel fuel, 5% RME and 10% higher alcohols under low load conditions (4 bar IMEP). During these experiments, different external EGR levels were applied while the injection timing was chosen in a way to keep the location of 50% heat release constant. Emission analysis results were in accordance with widely known correlations: Increasing EGR rates lowered NOx emissions. This is explained by a decrease of global air-fuel ratio entailing longer ignition delay. Local gas-fuel ratio increases during ignition delay and local combustion temperature is lowered. Exhaust gas analysis indicated further a strong increase of CO, PM and unburned HC emissions at high EGR levels. This resulted in lower combustion efficiency. PM emissions however, decreased above 50% EGR which was also in accordance with previously reported results. Besides those similar trends, fuel dependent differences in indicated thermal efficiency as well as CO, HC, NOx and especially PM emissions were observed. These differences were evaluated by detailed heat release analysis and explanation models based upon fuel characteristics as fuel viscosity and fuel distillation curve. Fuel spray evaporation and heat release were influenced by these fuel characteristics. Due to these characteristics it was concluded that RME has a higher tendency to form fuel rich zones at low load conditions than the other tested fuel types. Moreover it was found that improved fuel spray vaporisation is an option to improve exhaust emissions at low load conditions. (Less)

Analysis of Smokeless Spray Combustion in a Heavy-Duty Diesel Engine by Combined Simultaneous Optical Diagnostics

A heavy-duty diesel engine operating case producing no engine-out smoke was studied using combined simultaneous optical diagnostics. The case was close to a typical low-load modern diesel operating point without EGR. Parallels were drawn to the conceptual model by Dec and results from high-pressure combustion vessels. Optical results revealed that no soot was present in the upstream part of the jet cross-section. Soot was only observed in the recirculation zones close to the bowl perimeter. This indicated very slow soot formation and was explained by a significantly higher air entrainment rate than in Decs study. The local fuel-air equivalence ratio, Φ, at the lift-off length was estimated to be 40% of the value in Decs study. The lower Φ in the jet produced a different Φ-T history, explaining the soot results. The increased air entrainment rate was mainly due to smaller nozzle holes and increased TDC density. Furthermore, increased injection pressure was believed to reduce the residence time in the jet, thus reducing the soot formation. OH was detected at the periphery of the jet, upstream of the location where fuel started to react on the jet centerline. The OH region extended relatively far into the jet, further supporting the conclusion of a less fuel-rich jet in the current case. Partially oxidized fuel (POF) was found at the center of the jet, downstream of the lift-off position. This indicated that the temperature needed to start chemical reactions inside the jet had not been obtained at the lift-off position. The high-temperature reaction zone at the periphery thus added heat over a distance before POF was observed on the centerline.

Model Predictive Control of a Combined EGR/SCR HD Diesel Engine

Materials Noise, Vibration and Harshness Parts and Components Power and Propulsion Quality, Reliability and Durability Safety Tests and Testing Transportation Systems Vehicles and Performance Other Options Papers by Event SAE Home > Papers> By Event> SAE 2010 World Congress & Exhibition Model Predictive Control of a Combined EGR/SCR HD Diesel Engine Date Published: 2010-04-12Paper Number: 2010-01-1175 DOI: 10.4271/2010-01-1175 Author(s): Claes Westerlund - Scania CV AB Bjorn Westerberg - Scania CV AB Ingemar Odenbrand - Lund Univ. Rolf Egnell - Lund Univ. View All CollapseAbstract Achieving upcoming HD emissions legislation, Euro VI / EPA 10, is a challenge for all engine manufacturers. A likely solution to meet the NO x limit is to use a combination of EGR and SCR. Combining these two technologies poses new challenges and possibilities when it comes to optimization and calibration.

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.

Quantitative Imaging of Equivalence Ratios in DME Sprays Using a Chemically Preheated Combustion Vessel

Dimethyl Ether (DME) has proved to be a promising fuel for diesel engines. It virtually eliminates particulate emissions and reduces the formation of nitrogenous oxides, without negatively affecting engine efficiency. Obtaining a deeper understanding of the mechanisms behind these properties is thus highly desirable. Various authors have suggested that the low NO emissions associated with DME are an effect of the mixing conditions, which are thought to differ from those of diesel sprays. To examine this, laser-Rayleigh imaging was employed for quantitative measurement of the local equivalence ratios in DME sprays. The quantitative images were analyzed using a statistical approach, in which probability distributions of ϕ -values for burning and for non-reacting sprays were compared. It was concluded that the diffusion flame is established in the stoichiometeric or slightly lean regions of the spray. Measurements were performed in an isochoric combustion vessel chemically preheated by igniting a lean mixture of CO and oxygen-enriched air. A multizone combustion model was used to analyze the DME combustion and the effects of preheating on the vessel atmosphere. The benefits and drawbacks of this set-up are discussed. (Less)

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)

Laser-Rayleigh Imaging of DME Sprays in an Optically Accessible DI Diesel Truck Engine

Laser-Rayleigh imaging has been employed to measure the relative fuel concentration in the gaseous jet region of DME sprays. The measurements were performed in an optically accessible diesel truck engine equipped with a common rail injection system. A one-hole nozzle was used to guarantee that the recorded pressure history was associated with the heat release in the imaged spray. To compensate for the low compression ratio in the modified engine the inlet air was preheated. Spray development was studied for two levels of preheating, from the start of injection to the point where all fuel was consumed. The results indicate that there is a strong correlation between the amount of unburned fuel present in the cylinder and the rate of heat release at a given time. The combustion can not be described as purely premixed or purely mixing-controlled at any time, but always has an element of both. After all fuel appears to have vanished there is still an extended period of heat release. This indicates a rich combustion yielding combustible products.