Refine Your Search

Search Results

Viewing 1 to 13 of 13
Technical Paper

A Novel Model for Computing the Trapping Efficiency and Residual Gas Fraction Validated with an Innovative Technique for Measuring the Trapping Efficiency

2008-09-09
2008-32-0003
The paper describes a novel method for calculating the residual gas fraction and the trapping efficiency in a 2 stroke engine. Assuming one dimensional compressible flow through the inlet and exhaust ports, the method estimates the instantaneous mass flowing in and out from the combustion chamber; later the residual gas fraction and trapping efficiency are estimated combining together the perfect displacement and perfect mixing scavenging models. It is assumed that when the intake port opens, the fresh mixture is pushing out the burned charge without any mixing and after a multiple of the time needed for the largest eddy to perform one rotation, the two gasses are instantly mixed up together and expelled. The result is a very simple algorithm that does not require much computational time and is able to estimate with high level of precision the trapping efficiency and the residual gas fraction in 2 stroke engines.
Technical Paper

Influence of the Wall Temperature and Combustion Chamber Geometry on the Performance and Emissions of a Mini HCCI Engine Fueled with Diethyl Ether

2008-04-14
2008-01-0008
Nowadays for small-scale power generation there are electrochemical batteries and mini engines. Many efforts have been done for improving the power density of the batteries but unfortunately the value of 1 MJ/kg seems to be asymptotic. If the energy source is an organic fuel which has an energy density of around 29 MJ/kg with a minimum overall efficiency of only 3.5%, this device would surpass the batteries. This paper is the fifth of a series of publications aimed to study the HCCI combustion process in the milli domain at high engine speed in order to design and develop VIMPA, Vibrating Microengine for Low Power Generation and Microsystems Actuation. Previous studies ranged from general characterization of the HCCI combustion process by using metal and optical engines, to more specific topics for instance the influence of the boundary layer and quenching distance on the quality of the combustion.
Technical Paper

Improving Ion Current Feedback for HCCI Engine Control

2007-10-29
2007-01-4053
In HCCI you do not have the same control of the combustion like in SI and Diesel engines. Controlling the start of a combustion event is a difficult task and requires feedback from previous cycles. This feedback can be retrieved from ion current measurements. By applying a voltage over the spark gap, ions will lead a current and a signal that represents the combustion in the cylinder will be retrieved. Voltages of 450 V were used. The paper describes a new method to enhance the combustion phasing from the Ion current trace in HCCI engines. The method is using the knowledge of how the signal should look. This is known due to the fact that the shape of the ion current signal is similar from cycle to cycle. This new observation is shown in the paper. Also the correlation between the ion current and CA50 was studied. Later the signals have been used for combustion feedback.
Technical Paper

Influence of Inlet Temperature and Hot Residual Gases on the Performances of a Mini High Speed Glow Plug Engine

2006-11-13
2006-32-0057
Nowadays the power supplying systems have a fundamental importance for all small and portable devices. For low power applications, there are two main ways for producing power: electrochemical batteries and mini engines. Even though in recent years many developments have been carried out in improving the design of batteries, the energy density of 1MJ/kg seems to be an asymptotic value. If the energy source is a hydrocarbon fuel, whose energy density is 46 MJ/kg, with an overall efficiency of only 2.5 % it is possible to surpass the electrochemical batteries. On the other hand, having a mini engine, as energy source, implies three main problems: vibrations, noise and emissions. A light (230 g) model airplane engine with a displacement volume of 4.11 cm3 and a geometrical compression ratio of 13.91 has been studied. The work carried out in this paper can be divided basically in three parts.
Technical Paper

Multi-Output Control of a Heavy Duty HCCI Engine Using Variable Valve Actuation and Model Predictive Control

2006-04-03
2006-01-0873
Autoignition of a homogeneous mixture is very sensitive to operating conditions, therefore fast control is necessary for reliable operation. There exists several means to control the combustion phasing of an Homogeneous Charge Compression Ignition (HCCI) engine, but most of the presented controlled HCCI result has been performed with single-input single-output controllers. In order to fully operate an HCCI engine several output variables need to be controlled simultaneously, for example, load, combustion phasing, cylinder pressure and emissions. As these output variables have an effect on each other, the controller should be of a structure which includes the cross-couplings between the output variables. A Model Predictive Control (MPC) controller is proposed as a solution to the problem of load-torque control with simultaneous minimization of the fuel consumption and emissions, while satisfying the constraints on cylinder pressure.
Technical Paper

Combustion Chamber Wall Temperature Measurement and Modeling During Transient HCCI Operation

2005-10-24
2005-01-3731
In this paper the combustion chamber wall temperature was measured by the use of thermographic phosphor. The temperature was monitored over a large time window covering a load transient. Wall temperature measurement provide helpful information in all engines. This temperature is for example needed when calculating heat losses to the walls. Most important is however the effect of the wall temperature on combustion. The walls can not heat up instantaneously and the slowly increasing wall temperature following a load transient will affect the combustion events sucseeding the transient. The HCCI combustion process is, due to its dependence on chemical kinetics more sensitive to wall temperature than Otto or Diesel engines. In depth knowledge about transient wall temperature could increase the understanding of transient HCCI control. A “black box” state space model was derived which is useful when predicting transient wall temperature.
Technical Paper

Variable Valve Actuation for Timing Control of a Homogeneous Charge Compression Ignition Engine

2005-04-11
2005-01-0147
Autoignition of a homogeneous mixture is very sensitive to operating conditions. Therefore fast combustion phasing control is necessary for reliable operation. There are several means to control the combustion phasing of a Homogeneous Charge Compression Ignition (HCCI) engine. This paper presents cycle-to-cycle cylinder individual control results from a six-cylinder HCCI engine using a Variable Valve Actuation (VVA) system. As feedback signal, the crank angle for 50% burned, based on cylinder pressure, is used. Three control structures are evaluated, Model Predictive Control (MPC), Linear Quadratic Gaussian control (LQG) and PID control. In the control design of the MPC and LQG controller, dynamic models obtained by system identification were used. Successful experiments were performed on a port-injected six-cylinder heavy-duty Diesel engine operating in HCCI mode.
Technical Paper

Lean Burn Natural Gas Operation vs. Stoichiometric Operation with EGR and a Three Way Catalyst

2005-04-11
2005-01-0250
Exhaust Emissions from lean burn natural gas engines may not always be as low as the potential permits, especially engines with open loop lambda control. These engines can produce much higher emissions than a comparable diesel engine without exhaust gas after treatment. Even if the engine has closed loop lambda control, emissions are often unacceptably high for future emission regulations. A three way catalyst is, today, the best way to reduce hazardous emissions. The drawback is that the engine has to operate with a stoichiometric mixture and this leads to; higher heat losses, higher pumping work at low to medium loads, higher thermal stress on the engine and higher knock tendency (requiring lower compression ratio, and thus lower brake efficiency). One way to reduce these drawbacks is to dilute the stoichiometric mixture with EGR. This paper compares lean burn operation with operation at stoichiometric conditions diluted with EGR, and using a three way catalyst.
Technical Paper

Cycle-to-Cycle Control of a Dual-Fuel HCCI Engine

2004-03-08
2004-01-0941
A known problem of the HCCI engine is its lack of direct control and its requirements of feedback control. Today there exists several different means to control an HCCI engine, such as dual fuels, variable valve actuation, inlet temperature and compression ratio. Independent of actuation method a sensor is needed. In this paper we perform closed-loop control based on two different sensors, pressure and ion current sensor. Results showing that they give similar control performance within their operating range are presented. Also a comparison of two methods of designing HCCI timing controller, manual tuning and model based design is presented. A PID controller is used as an example of a manually tuned controller. A Linear Quadratic Gaussian controller exemplifies model based controller design. The models used in the design were estimated using system identification methods. The system used in this paper performs control on cycle-to-cycle basis. This leads to fast and robust control.
Technical Paper

The Potential of Using the Ion-Current Signal for Optimizing Engine Stability - Comparisons of Lean and EGR (Stoichiometric) Operation

2003-03-03
2003-01-0717
Ion current measurements can give information useful for controlling the combustion stability in a multi-cylinder engine. Operation near the dilution limit (air or EGR) can be achieved and it can be optimized individually for the cylinders, resulting in a system with better engine stability for highly diluted mixtures. This method will also compensate for engine wear, e.g. changes in volumetric efficiency and fuel injector characteristics. Especially in a port injected engine, changes in fuel injector characteristics can lead to increased emissions and deteriorated engine performance when operating with a closed-loop lambda control system. One problem using the ion-current signal to control engine stability near the lean limit is the weak signal resulting in low signal to noise ratio. Measurements presented in this paper were made on a turbocharged 9.6 liter six cylinder natural gas engine with port injection.
Technical Paper

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

2003-03-03
2003-01-0743
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.
Technical Paper

Hydrogen Addition For Improved Lean Burn Capability of Slow and Fast Burning Natural Gas Combustion Chambers

2002-10-21
2002-01-2686
One way to extend the lean burn limit of a natural gas engine is by addition of hydrogen to the primary fuel. This paper presents measurements made on a one cylinder 1.6 liter natural gas engine. Two combustion chambers, one slow and one fast burning, were tested with various amounts of hydrogen (0, 5, 10 and 15 %-vol) added to natural gas. Three operating points were investigated for each combustion chamber and each hydrogen content level; idle, part load (5 bar IMEP) and 13 bar IMEP (simulated turbocharging). Air/fuel ratio was varied between stoichiometric and the lean limit. For each operating point, a range of ignition timings were tested to find maximum brake torque (MBT) and/or knock. Heat-release rate calculations were made in order to assess the influence of hydrogen addition on burn rate. Addition of hydrogen showed an increase in burn rate for both combustion chambers, resulting in more stable combustion close to the lean limit.
Technical Paper

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

2002-03-04
2002-01-0111
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.
X