Magnus Lewander

Investigation of the Combustion Characteristics with Focus on Partially Premixed Combustion in a Heavy Duty Engine

Partially Premixed Combustion (PPC) has shown its potential by combining high combustion controllability with emission characteristics that are close to those of an HCCI engine. In order to get PPC the ignition delay needs to be long enough for the fuel and air to mix prior to combustion. This can be achieved by injecting the fuel sufficiently early while running with high EGR.In order to find out where and how PPC occurs a map that shows the changes in combustion characteristics with injection timing and EGR was created. The combustion characteristics were studied in a six cylinder heavy duty engine where the Start of Injection (SOI) was swept from early to late injection over a wide range of EGR levels. The emissions were monitored during the sweeps and in the most promising regions, with low emissions and high efficiency, additional changes in injection pressure and engine speed were applied to get a more versatile picture of the combustion. (Less)

Extending the Operating Region of Multi-Cylinder Partially Premixed Combustion using High Octane Number Fuel

Partially Premixed Combustion (PPC) is a combustion concept by which it is possible to get low smoke and NOx emissions simultaneously. PPC requires high EGR levels to extend the ignition delay so that air and fuel mix prior to combustion to a larger extent than with conventional diesel combustion. This paper investigates the operating region of single injection PPC for three different fuels; Diesel, low octane gasoline with similar characteristics as diesel and higher octane standard gasoline. Limits in emissions are defined and the highest load that fulfills these requirements is determined. The investigation shows the benefits of using high octane number fuel for Multi-Cylinder PPC. With high octane fuel the ignition delay is made longer and the operating region of single injection PPC can be extended significantly. Experiments are carried out on a multi-cylinder heavy-duty engine at low, medium and high speed. (Less)

Evaluation of the Operating Range of Partially Premixed Combustion in a Multi Cylinder Heavy Duty Engine with Extensive EGR

Partially Premixed Combustion (PPC) is a combustion concept by which it is possible to get low smoke and NOx emissions simultaneously. PPC requires high EGR levels and injection timings sufficiently early or late to extend the ignition delay so that air and fuel mix extensively prior to combustion. This paper investigates the operating region of single injection diesel PPC in a multi cylinder heavy duty engine resembling a standard build production engine. Limits in emissions and fuel consumption are defined and the highest load that fulfills these requirements is determined. Experiments are carried out at different engine speeds and a comparison of open and closed loop combustion control are made as well as evaluation of an extended EGR-cooling system designed to reduce the EGR temperature. In this study the PPC operating range proved to be limited. The highest loads that fulfilled the emission criteria correspond to 30% of maximum load for conventional combustion at low speed and 21% of maximum load for conventional combustion at high speed. The effect of changes in combustion control was small while a reduced EGR temperature could increase the operating range significantly. (Less)

Investigation and Comparison of Multi Cylinder Partially Premixed Combustion Characteristics for Diesel and Gasoline Fuels

Partially Premixed Combustion is a concept able to combine low smoke and NOx emissions with high combustion controllability and efficiency. It is of interest to be able to utilize PPC in a large operating region in order to meet the Euro VI emission legislation without relying on NOx aftertreatment. This paper investigates the differences in PPC characteristics for three fuels; Diesel Swedish Mk 1, Low Octane Gasoline (70 Octane) and US Standard Gasoline (87 Octane). Engine operating conditions, combustion characteristics, emissions and efficiency are in focus. The experiments were carried out at a range of operating points on a Volvo MD13 which is a six-cylinder heavy-duty engine. At each operating point three combinations of EGR level and λ-value were evaluated. 1. High EGR/High λ, 2. High EGR/Reduced λ, and 3. Reduced EGR/High λ. Further, for all these three conditions, four combustion timings were tested reaching from advanced combustion timing at 3 CAD ATDC to retarded combustion timing at 9 CAD ATDC. The indicated load and the combustion timing were controlled cylinder individually by a feedback controller. (Less)

A Correlation Analysis of the Roles of Soot Formation and Oxidation in a Heavy-Duty Diesel Engine

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. (Less)

Steady state fuel consumption optimization through feedback control of estimated cylinder individual efficiency

Engine efficiency is often controlled in an indirect way through combustion timing control. This requires a priori knowledge of where to phase the combustion for different operating points and conditions. With cylinder individual efficiency estimation, control strategies aiming directly at fuel consumption optimization can be developed. It has previously been shown that indicated efficiency can be estimated using the cylinder pressure trace. This paper presents a method to use the estimated efficiency as a feedback variable in an extremum seeking control strategy for online steady state fuel consumption optimization. The experimental results show that the controller manages to find the maximum brake torque region at the given operating point both with and without external excitation.

Model Predictive Control of Partially Premixed Combustion

Partially premixed combustion is a compression ignited combustion strategy where high exhaust gas recirculation (EGR) levels in combination with early or late injection timing result in a prolonged ignition delay yielding a more premixed charge than with conventional diesel combustion. With this concept it is possible to get low smoke and NOx emissions simultaneously. Accurate control of injection timing and injection duration is however necessary in order to achieve this favorable mode of combustion. This chapter presents a method for controlled PPC operation. The approach is to control the time between end of injection and start of combustion which if positive yields sufficient premixing. Model Predictive Control was used to control the engine which was modeled using System Identification. The results show that it is possible to assure PPC operation in the presence of both speed/load transients and EGR disturbances.

Cylinder Individual Efficiency Estimation for Online Fuel Consumption Optimization

Engine efficiency is often controlled in an indirect way through combustion timing control. This requires a priori knowledge of where to phase the combustion jiff different operating points and conditions. With cylinder individual efficiency estimation, control strategies aiming directly at fuel consumption optimization can be developed. This paper presents a method to estimate indicated efficiency using the cylinder pressure trace as input. The proposed method is based on a heat release calculation that takes heat losses into account implicitly using an estimated, CAD resolved polytropic exponent. Experimental results from a multi-cylinder engine show that with this approach, the estimated efficiency error is within 5% for all operating points tested. The final part of the paper is a discussion of how to use the efficiency estimation for feedback control. Different control concepts are presented as well as suggestions on how to handle the non-linear connection between combustion timing and indicated efficiency. (Less)

Transient Control of Combustion Phasing and Lambda in a Six-Cylinder Port-Injected Natural-Gas Engine

Fuel economy and emissions are the two central parameters in heavy duty engines. High exhaust gas recirculation rates combined with turbocharging has been identified as a promising way to increase the maximum load and efficiency of heavy duty spark ignition engines. With stoichiometric conditions, a three way catalyst can be used, which keeps the regulated emissions at very low levels. The Lambda window, which results in very low emissions, is very narrow. This issue is more complex with transient operation, resulting in losing brake efficiency and also catalyst converting efficiency. This paper presents different control strategies to maximize the reliability for maintaining efficiency and emissions levels under transient conditions. Different controllers are developed and tested successfully on a heavy duty six-cylinder port injected natural gas engine. Model predictive control was used to control lambda, which was modeled using system identification. Furthermore, a proportional integral regulator combined with a feedforward map for obtaining maximum brake torque timing was applied. The results show that excellent steady-state and transient performance can be achieved.

The novel SCR and PNA exhaust gas after treatment systems for diesel passenger cars

The future emissions legislation for diesel passenger cars is likely to include more dynamic test cycles than we have today, such as the WLTP and RDE cycles in the EU and challenging SULEV legislations in the USA. In order to meet these emissions legislation more complex exhaust gas after treatment systems are needed.