Carl Wilhelmsson

Operation strategy of a Dual Fuel HCCI Engine with VGT

HCCI combustion is well known and much results regarding its special properties have been published. Publications comparing the performance of different HCCI engines and comparing HCCI engines to conventional engines have indicated special features of HCCI engines regarding, among other things, emissions, efficiency and special feedback-control requirements. This paper attempts to contribute to the common knowledge of HCCI engines by describing an operational strategy suitable for a dual-fuel port-injected Heavy Duty HCCI engine equipped with a variable geometry turbo charger. Due to the special properties of HCCI combustion a specific operational strategy has to be adopted for the engine operation parameters (in this case combustion phasing and boost pressure). The low exhaust temperature of HCCI engines limits the benefits of turbo charging and causes pumping losses which means that “the more the merrier” principle does not apply to intake pressure for HCCI engines. It is desirable not to use more boost pressure than necessary to avoid excessively rapid combustion and/or emissions of NOx. It is also desirable to select a correct combustion phasing which, like the boost pressure, has a large influence on engine efficiency. The optimization problem that emerges between the need for boost pressure to avoid noise and emissions and, at the same time, avoiding an extensive decrease of efficiency because of pumping losses is the topic of this paper. The experiments were carried out on a 12 liter Heavy Duty Diesel engine converted to pure HCCI operation. Individually injected natural gas and n-Heptane with a nominal injection ratio of 85% natural gas and the rest n-Heptane (based on heating value) was used as fuel. The engine was under feedback combustion control during the experiments. (Less)

The Effect of Displacement on Air-Diluted Multi-Cylinder HCCI Engine Performance

The main benefit of HCCI engines compared to SI engines is improved fuel economy. The drawback is the diluted combustion with a substantially smaller operating range if not some kind of supercharging is used. The reasons for the higher brake efficiency in HCCI engines can be summarized in lower pumping losses and higher thermodynamic efficiency, due to higher compression ratio and higher ratio of specific heats if air is used as dilution. In the low-load operating range, where HCCI today is mainly used, other parameters as friction losses, and cooling losses have a large impact on the achieved brake efficiency. To initiate the autoignition of the in-cylinder charge a certain temperature and pressure have to be reached for a specific fuel. In an engine with high in-cylinder cooling losses the initial charge temperature before compression has to be higher than on an engine with less heat transfer. The heat transfer to the combustion chamber walls is affected by parameters such as area-to-volume ratio and in-cylinder gas motion, i.e., turbulence. In this paper the performance of three multi-cylinder HCCI engines with different displacements are compared. The engines are a five-cylinder 1.6dmu3 VCR engine, a four-cylinder 2.0dmu3 engine, and a six-cylinder 11.7dmu3 truck engine. All engines are port fuel injected and run with a RON91/MON82 gasoline. Combustion phasing is mainly controlled with inlet air temperature. The engines have about the same indicated efficiency but different brake efficiency. The truck engine has 32.3% brake efficiency at 2 bar BMEP, followed by the 2.0dmu3 engine with 29.8%, and the 1.6dmu3 VCR engine with only 24.4%. (Less)

A Fast Physical NOx Model Implemented on an Embedded System

This paper offers a two-zone, physical, NOx model with low computational cost, implemented in C on an embedded system. The model is able to compute NOx-emission formation with high time resolution during an engine cycle. To do this the model takes cylinder pressure and injected fuel amount as inputs and produces NO concentration as output. The model as such is not new, nevertheless the physical background of the model as well as the equations upon which the model is based had to be briefly described to facilitate the understanding of the subsequent work. The main part of the paper is devoted to the process of developing an algorithm implementing the described model, techniques used and issues encountered are described. The resulting algorithm was implemented in C and tested on an embedded ARM processor. For the sake of implementation, parts of the algorithm had to be pre-computed and stored in tables, allowing significant acceleration of the computations. Since the model is non-linear, exponentially spaced tables had to be developed in order to successfully tabulate the parts needed without consuming too much memory. Much of the methods presented are also applicable in a variety other applications when it is desirable to implement fast versions of complex algorithms and models. The outcome regarding computation speed and memory needed is discussed. The final result is a low-cost NOx model, which is able to compute several orders of magnitude faster than NOx models known so far, implemented in C on an embedded system.

An Ultra High Bandwidth Automotive Rapid Prototype System

For developers of automotive control, prototyping and initial tests are a hassle. Commercial solutions are available but the price and especially the price/performance ratio opens the field for more cost effective solutions. Automotive rapid prototype systems seen so far are mainly processor based systems with standard interrupt driven measurement and actuation. Control systems based on high time resolution measurements of for example cylinder pressure are difficult to implement using these systems, neither is it possible to implement controller loops with an extremely high bandwidth in combination with expensive algorithms. Measurement and actuation within the same engine cycle, In Cycle Control (ICC) are not possible. The proposed system is based on a mixed system consisting of one standard x86 processor which is configured through Simulink and a reconfigurable application specific integrated circuit (an FPGA) configured either by relevant FPGA design tools or by Simulink. This layout of the rapid prototype system enables the designer to implement either ICC with very high bandwidth (only limited by the capacity of the injection system) or betweencycle control with medium bandwidth. The aim of this paper is to describe one possible configuration of such a system and to discuss the possible performance outcome of the final system. (Less)

A Physical Two-Zone NOx Model Intended for Embedded Implementation

This paper offers a two-zone NOx model suitable for vehicle on-board, on-line implementation. Similar NOx modeling attempts have previously been undertaken. The hereby suggested method does however offer clear and important benefits over the previously methods, utilizing a significantly different method to handle temperature calculations within the (two) different zones avoiding iterative computation. The new method significantly improves calculation speed and, most important of all, reduces implementation complexity while still maintaining reasonable accuracy and the physical interpretation of earlier suggested methods. The equations commonly used to compute NOx emissions is also rewritten in order to suit a two-zone NOx model. An algorithm which can be used to compute NOx emissions is presented and the intended contribution of the paper is a NOx model, implementation feasible for an embedded system, e.g. embedded processor or embedded electronic hardware (FPGA). For that purpose parts of the algorithm can be pre-computed and stored in tables allowing significant acceleration of the computation.

A Physical Two-Zone NOxModel Intended for Embedded Implementation

This paper offers a two-zone NOx model suitable for vehicle on-board, on-line implementation. Similar NOx modeling attempts have previously been undertaken. The hereby suggested method does however offer clear and important benefits over the previously methods, utilizing a significantly different method to handle temperature calculations within the (two) different zones avoiding iterative computation. The new method significantly improves calculation speed and, most important of all, reduces implementation complexity while still maintaining reasonable accuracy and the physical interpretation of earlier suggested methods. The equations commonly used to compute NOx emissions is also rewritten in order to suit a two-zone NOx model. An algorithm which can be used to compute NOx emissions is presented and the intended contribution of the paper is a NOx model, implementation feasible for an embedded system, e.g. embedded processor or embedded electronic hardware (FPGA). For that purpose parts of the algorithm can be pre-computed and stored in tables allowing significant acceleration of the computation.