Smoking machine

This application is a National Stage filing of International Application PCT/GB2006/001073, filed Mar. 23, 2006, claiming priority to United Kingdom Application No. 0506120.5, filed Mar. 24, 2005, entitled “SMOKING MACHINE”. The present application claims priority to PCT/GB2006/001073, and to United Kingdom Application No. 0506120.5, and both references are expressly incorporated by reference herein, in their entireties.

The present invention relates to a smoking machine for smoking a smoking article, such as a cigarette or cigar, in order to analyse the composition of a smoke stream from the smoking article.

It is well known that the process of smoking cigarettes and cigars liberates many chemicals in the form of gases, vapours or particulates that are either harmful or noxious in character. These chemicals are formed as the result of the pyrolysis or partial pyrolysis of the article being smoked. The amount liberated by a particular cigarette is dependant upon the method of smoking, the tobacco blend, the packing of the tobacco, the permeability of the paper used in construction and any filter system, amongst other factors. Because there are so many variables involved in the process of producing smoke it is necessary to analyse actual smoke streams to determine the delivery of these gases and vapours.

Analysis of the composition of the smoke stream is important for two reasons. Firstly, the manufacturer of smoking articles may use smoke composition as a measure of the acceptability of the product, or as a quality control measure. Secondly, routine analysis of smoking articles is required by legislation for reporting to regulatory bodies to ensure the products sold to the consumer do not exceed maximum levels of particular hazardous substances.

The normal method employed for the analysis of smoke composition involves the use of a mechanical smoking machine with well defined smoking characteristics. The use of such a machine fixes a set of process variables concerned with smoke generation, so the variables affecting the formation of gases and vapours is then restricted to the design, construction and composition of the smoking article. There are two types of smoke formed, main stream which is formed when air is passed through the cigarette as a breath is drawn, and side stream, where the cigarette burns between puffs. The two smoke streams are likely to differ in composition as the temperature of pyrolysis will differ between the two modes.

The smoke so formed is normally captured in a fibre pad which is then removed for analysis. The removed capture pad requires a series of chemical extractions and analysis that may take many hours, considerable labour and sophisticated analytical instruments. Gases that are not captured by the pad may be bubbled through impingers to trap the gas chemically or physically, or the gases may be measured using sophisticated analytical instruments dedicated for the purpose.

The known method of analysing a smoke stream is characterised by the complexity of capture and analysis and by the time delay between smoking and analysing the captured gases. There is also a potential source of bias and error as the vapour or gas may be imperfectly captured or may be involved in a chemical reaction affected by thermodynamic factors. Whilst this is generally acceptable for trace elements, routine analysis for major components may be hampered by this slow process.

According to an aspect of the present invention there is provided a smoking machine for smoking a smoking article, the smoking machine comprising an electrochemical cell for analysing the composition of a smoke stream from the smoking article.

By using an electrochemical cell (sometimes known as a fuel cell) in a smoking machine, the present invention may provide the advantage that a gas or vapour phase chemical can be analysed directly in real time without the need for pre-conditioning or preparation.

The electrochemical cell is preferably arranged to detect a gas in the smoke stream. For example, the electrochemical cell may be arranged to oxidize or to reduce the gas to be detected. The electrochemical cell may be arranged to output an electrical signal indicative of the presence or amount of the gas to be detected. The smoking machine may further comprise an amplifier for amplifying the output of the electrochemical cell.

In order to carry out an analysis of the smoke stream, the smoking machine may further comprise processing means for processing the output of the electrochemical cell. The processing means may be arranged to log an amount of a detected gas over time as the smoking article is smoked, in order to build up a profile of the concentration of the gas through the smoking run. The processing means may be a processor co-located with the electrochemical cell, or it may be separate from the electrochemical cell. For example the processing means may be a separate computer which is arranged to log, analyse and display the data.

The concentration of a particular gas and the manner in which the concentration changes with time through a smoking run will, within predefined limits, be characteristic of the cigarette brand smoked. Thus a characteristic profile of the smoke generated for that brand may be developed for a standard set of mechanical smoking parameters. By comparing the characteristic profile with the profile of a cigarette under test, quality control or counterfeit detection may be performed on the test cigarette. Therefore the processing means may be arranged to store a profile of an amount of gas over time for a known smoking article and to compare the logged profile with the stored profile.

The electrochemical cell may be located in a chamber which is in communication with the smoke stream. The chamber may be a dedicated analysis chamber located in the path of the smoke stream. Such an arrangement may allow a conventional smoking machine to be modified simply by inserting the analysis chamber into the path of the smoke stream. Alternatively the chamber may be a filter pad chamber. This may allow the chamber to perform the dual functions of holding a filter pad and holding the electrochemical cell, which may allow the machine to be more compact and cheaper to manufacture.

The chamber may comprise a sub-chamber for accommodating the electrochemical cell. The sub-chamber may comprise a passageway which is selected in size to control the flow rate through the sub-chamber. Alternatively or in addition the smoking machine may further comprise means for introducing an additional gas, such as air, into the sub-chamber so as to dilute the smoke stream impinging on the electrochemical cell. These measures may help to ensure that the correct concentration of the gas to be detected impinges on the electrochemical cell.

Preferably the smoking machine comprises a plurality of electrochemical cells. Two or more electrochemical cells may in some cases be the same or similar. However two or more electrochemical cells are preferably sensitive to different gases and/or have a different sensitivity to a particular gas. This can allow the cells to provide simultaneous information about more than one substance in the smoke stream.

Each of the electrochemical cells may be located in a separate sub-chamber. Two or more sub-chambers may then comprise passageways of different sizes to control the flow rates through the sub-chambers. This may help to compensate for different sensitivities of the different electrochemical cells. Furthermore, two or more sub-chambers may be arranged to dilute the smoke stream by a different amount, which again may help to compensate for different sensitivities.

As the detection of a gas by an electrochemical cell may not be perfectly specific, the combination of a number of complimentary cells that have cross interferences to other gases can be used to determine more accurately the concentration of a specified gas. Therefore the smoking machine may further comprise processing means for determining a cross interference between different gases based on the output of two or more electrochemical cells. For example, the processor may be arranged to solve a set of at least two simultaneous equations involving at least two measurements and at least two unknowns. The equations may be linear or non-linear. Any appropriate technique may be used to solve the equations, such as direct or iterative methods.

Two electrochemical cells which are both sensitive to the same gas may be located one on either side of a filter pad. This arrangement may provide information concerning the efficiency of the filter pad. In this case processing means may be arranged to compare a concentration of a gas detected before the filter pad with a concentration of the gas detected after the filter pad.

The smoking machine may further comprise a gas permeable membrane located between the smoke stream and the electrochemical cell. Such a membrane may allow the gas of interest to pass through, but block the passage of particulates, condensates and unwanted solid and liquid materials. The membrane may be removable. The membrane may then perform the function of a particulate and condensate collection pad removing all particulates and condensates from the smoke stream. These collected materials may be extracted from the membrane for future analysis. Where a plurality of electrochemical cells are provided, some cells may be provided with a membrane and some without, or different cells may be provided with different membranes, in order to ensure that the gases of interest impinge on the electrochemical cells in the desired concentrations.