Jan-Ola Olsson

Closed-Loop Control of an HCCI Engine

This paper presents a strategy for closed-loop control of a multi-cylinder turbocharged Homogeneous Charge Compression Ignition (HCCI) engine. A dual fuel port injection system allows control of combustion timing and load individually for each cylinder. The two fuels used are isooctane and n-heptane, which provides a wide range of autoignition properties. Cylinder pressure sensors provide feedback and information regarding combustion. The angle of 50% heat release is calculated in real time for each cycle and used for timing feedback. Inlet air preheating is used at low loads to maintain a high combustion efficiency.

Compression Ratio Influence on Maximum Load of a Natural Gas Fueled HCCI Engine

This paper discusses the compression ratio influence on maximum load of a Natural Gas HCCI engine. A modified Volvo TD100 truck engine is controlled in a closed-loop fashion by enriching the Natural Gas mixture with Hydrogen. The first section of the paper illustrates and discusses the potential of using hydrogen enrichment of natural gas to control combustion timing. Cylinder pressure is used as the feedback and the 50 percent burn angle is the controlled parameter. Full-cycle simulation is compared to some of the experimental data and then used to enhance some of the experimental observations dealing with ignition timing, thermal boundary conditions, emissions and how they affect engine stability and performance. High load issues common to HCCI are discussed in light of the inherent performance and emissions tradeoff and the disappearance of feasible operating space at high engine loads. The problems of tighter limits for combustion timing, unstable operational points and physical constraints at high loads are discussed and illustrated by experimental results. Finally, the influence on operational limits, i.e., emissions peak pressure rise and peak cylinder pressure, from compression ratio at high load are discussed. (Less)

A Turbocharged Dual-Fuel HCCI Engine

A 6-cylinder truck engine is modified for turbocharged dual-fuel Homogeneous Charge Compression Ignition (HCCI) engine operation. Two different fuels, ethanol and n-heptane, are used to control the ignition timing. The objective of this study is to demonstrate high load operation of a full-size HCCI engine and to discuss some of the typical constraints associated with HCCI operation. This study proves the possibility to achieve high loads, up to 16 bar Brake Mean Effective Pressure (BMEP), and ultra-low NOdx emissions, using turbo charging and dual fuel. Although the system shows great potential, it is obvious that the lack of inlet air pre heating is a drawback at low loads, where combustion efficiency suffers. At high loads, the low exhaust temperature provides little energy for turbocharging, thus causing pump losses higher than for a comparable diesel engine. Design of turbocharger therefore, is a key issue in order to achieve high loads in combination with high efficiency. In spite of these limitations, brake thermal efficiencies and power rating close to those of the original diesel engine are achieved with significant reduction in NOdx emissions. The maximum efficiency is 41.2%, which is slightly lower than for the original diesel engine.

Boosting for High Load HCCI

Homogeneous Charge Compression Ignition (HCCI) holds great promises for good fuel economy and low emissions of NOdx and soot. The concept of HCCI is premixed combustion of a highly diluted mixture. The dilution limits the combustion temperature and thus prevents extensive NOdx production. Load is controlled by altering the quality of the charge, rather than the quantity. No throttling together with a high compression ratio to facilitate autoignition and lean mixtures results in good brake thermal efficiency. However, HCCI also presents challenges like how to control the combustion and how to achieve an acceptable load range. This work is focused on solutions to the latter problem. The high dilution required to avoid NOdx production limits the mass of fuel relative to the mass of air or EGR. For a given size of the engine the only way to recover the loss of power due to dilution is to force more mass through the engine. This paper shows that this can be done by the use of turbocharging or a mechanically driven compressor. The cost of forcing more air through the engine and the higher peak pressure requirements are discussed and quantified by simple engine modelling supported by experimental data. (Less)

The Effect of Cooled EGR on Emissions and Performance of a Turbocharged HCCI Engine

This paper discusses the effects of cooled EGR on a turbo charged multi cylinder HCCI engine. A six cylinder, 12 liter, Scania D12 truck engine is modified for HCCI operation. It is fitted with port fuel injection of ethanol and n-heptane and cylinder pressure sensors for closed loop combustion control. The effects of EGR are studied in different operating regimes of the engine. During idle, low speed and no load, the focus is on the effects on combustion efficiency, emissions of unburned hydrocarbons and CO. At intermediate load, run without turbocharging to achieve a well defined experiment, combustion efficiency and emissions from incomplete combustion are still of interest. However the effect on NOX and the thermodynamic effect on thermal efficiency, from a different gas composition, are studied as well. At high load and boost pressure the main focus is NOX emissions and the ability to run high mean effective pressure without exceeding the physical constraints of the engine. In this case the effects of EGR on boost and combustion duration and phasing are of primary interest. It is shown that CO, HC and NOX emissions in most cases all improve with EGR compared to lean burn. Combustion efficiency, which is computed based on exhaust gas analysis, increases with EGR due to lower emissions of CO and HC.

System identification and LQG control of variable-compression HCCI engine dynamics

The homogenous charge compression ignition (HCCI) combustion engine has potential to replace the spark ignition and compression ignition engines of today. One of the main problems in making the engine commercially attractive is the lack of direct means of controlling the ignition phasing. We investigate the potential of inlet air temperature as a means to ignition actuation. This article describes a method for system identification of the HCCI process, and development of an effective LQG regulator for the combustion process, Matlab and Simulink being used in computations and simulations.

Closed-loop System Identification of an HCCI Engine

Abstract Homogeneous Charge Compression Ignition (HCCI) is a promising but challenging combustion engine concept. The potential for good fuel economy and low emissions is high but the transient performance required for automotive applications presents a few problems still to be solved. The focus of this work is identification of the process dynamics. An ARX type model is fitted to input-output data. A method applicable under closed-loop control is suggested and demonstrated. The resulting models are evaluated in terms of the repeatability of model characteristics, prediction accuracy, residual characteristics and comparison to spectral models is made.