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Over the years, natural gas has been promoted as a clean-burning fuel, especially for transit buses. A decade ago one could claim that natural gas buses deliver significant emission benefits over diesel buses, especially regarding particulate emissions. The spread in nitrogen oxide emissions has always been significant for natural gas engines, high for lean-burn engines and low for three-way catalyst equipped stoichiometric engines. With the introduction of US 2010 and Euro VI (effective as of 2014) exhaust emission regulations, independent of the fuel, the regulated emissions of all engines have been brought close to zero level. This means that the advantage of natural gas as a clean fuel is diminishing, especially in a situation in which electric transit buses are also entering the market. The motivation to use natural gas could still be diesel fuel substitution and to some extent, also reduction of greenhouse gas emissions.

VTT (Technical Research Centre of Finland) has together with the Finnish energy company St1 tested different high-volume ethanol fuel (E85) samples in order to find the optimum composition for this fuel to perform satisfactorily in low ambient temperature driving conditions encountered in Finland quite frequently during the winter season. Altogether six different fuel compositions were evaluated, with 70 to 85 % of anhydrous bioethanol, and various different mixes of regular petrol components and some specific species like ETBE, butane, etc. As a reference, new Euro-quality 95 RON petrol with 10% ethanol was used. Volatility of each sample was adjusted according to test temperatures to match summer or winter condition and to ensure effortless start-up. Test results showed that the composition of the fuel had marked influence on emissions. The lower the test temperature was, the more distinctive were the differences.

Exhasut emissions were determined from a fleet of some 50 cars that have been in normal private ownership service in Finnish driving conditions. These represent typical Nordic climate with strongly varying ambient temperatures between summer and winter months. All cars were petrol-fuelled, and had an up-to-date emissions control system based on a three-way catalytic converter. Tested vehicles represented model years 1990 to 1996. They had odometer ratings at the time of testing ranging from a low of 10,000 km up to a high of 373,000 km. The emissions performance was assessed using U.S. FTP75 urban during schedule. Testing was carried out at normal ambient temperatures (+22...23° ...). The paper reports an assessment of typical emissions performance as a function of distance driven encountered from normal TWC cars that have been in day-to-day use under sometimes quite rigorous driving conditions.

Motor vehicles are seldom used in ambient conditions like those defined in current emission regulations. For example, most of the year average temperatures across Europe fall much below the range of legislative testing. Furthermore, it has been widely demonstrated that cold-starts at low ambient temperature increase the emissions. Therefore, there is a growing need to broaden the range of legislative emissions tests and set a separate low-ambient test with respective emission standards. This paper gives emissions test results form a joint research programme between Sweden and Finland. Altogether 11 late model gasoline-fueled TWC vehicles were tested at ambient temperatures of +22 and -7 °C using a variety of different driving cycles. Apart from the driving schedule, other test parameters like vehicle preconditioning, manual vs. automatic transmission and the effect of external cooling were studied and discussed.

Using fast FTIR-technology (Fourier Transform Infra-Red) to complement the normal regulated emission analysis, VTT Energy has performed exhaust emission measurements for several light-duty motor vehicles (passenger cars) representing a variety of current level technologies, mostly employing a three-way catalytic converter. Tests have been performed using standardized test procedures and driving cycles (U.S.EPA and ECE/EEC). Apart from the basic technology of the vehicle, ambient temperature has also been varied. Most of the tests are run at +20 to +22 °C ambient temperature, but additional tests have been carried out at ±0°C, -7 °C and even at -20 °C. Test results suggest that nitrous oxide output varies largely from vehicle to vehicle, and its is also dependent on the ambient temperature. Most significant factor, however, seems to be vehicle mileage, or rather catalyst activity, as already suggested in previous studies.

The widening use of three-way catalyst for emission control has brought an increasing number of vehicles employnig this tehcnology also to the areas of cold climate, like the Nordic countries. However, cold operating environment is found to derate the performance of a TWC system, as the guidelines for its desing are mainly set by the legislation, in which the test procedures have not taken into account low ambient conditions. This set is about to change, as the United States has recently introduced a low temperature emissions test with CO standard. Similar evolution has already began also in Europe.

Tight certification standards for new motor vehicles have always been the basestock for legislative efforts to control motor vehicle related air pollution. However, new additives need to be used when composing the formula for today's situation, where the relative contribution of new vehicles to the overall emissions is quickly diminishing and in-use performance is starting to play an increasingly important role. This paper outlines the general lay-out of the Finnish in-use control programme, which was started January 1, 1993. The choice of test procedure as well its initial verification are discussed. Determination and validation of the cut-points is also closely detailed. The main emphasis of the paper, however, lies in the practical experience gathered during the three-year planning and field testing phase that preceeded the introduction of the programme. Items that are typical for Finland, like cold ambient conditions, are more deeply discussed.

Cold operating environment has many kinds of negative effects on the use of automobiles. Low ambient temperature degrades start-up performance and increases fuel consumption. Hence, the amounts of exhaust emissions are also elevated. In particular, high concentrations of CO and HC are present in the exhaust. Cold-start derates especially the performance of a TWC type of emission reduction. Therefore, an increasing emphasis has been set to the testing of exhaust emissions even at sub-ambient temperatures, For this reason, US-EPA has recently revised US emission regulations by comprising an additional low ambient temperature (20°F = -7°C) test for CO emissions. Apart from the regulated components, other poisonous compounds have been detected from the exhausts, although usually in very small quantities, A cold-start may have an increasingly strong effect even to the emission of these substances.

Cold operating environment has many kinds of negative effects on the use of automobiles. Low ambient temperature degrades start-up performance and increases fuel consumption. Hence, the amount of harmful exhaust emissions is also elevated. In particular, high concentrations of carbon monoxide (CO) and unburned hydrocarbons (HC) are present. The continuously widening implementation of US-type emission regulations around the world has brought emission control technology based on the use of three-way catalyst (TWC) even to the Nordic countries having cold climate. Cold-start increases emissions from conventional cars, and especially the performance of TWC type of emission reduction has been shown to be quite susceptible to low ambient temperature. Therefore, an increasing emphasis has been set to the testing of exhaust emissions also at sub-normal temperatures, i.e. below the range of +20 …+30°C widely designated by the legislative procedures.

Previous work indicates that depending on the system, the increase in CO and HC emissions after a cold start at low ambient temperature can be 3 to 5 -fold compared to the operation at normal ambient conditions. The performance of a three-way catalyst system operating after a cold start at a low ambient temperature was found mainly to be governed by the rich mixture setting neccesitated by the poor evaporization of the fuel. This results in incorrect exhaust composition for the conversion point of view, as no oxygen is available. In proprietary engine tests carried out in a special cold test facility the emissions of CO and HC could be decreased by extending the idle or using block heater prior to the cold-start of the engine. Conversion of CO and HC was improved also by adding free oxygen into the exhaust. This was done by injecting air into the exhausts before the converter but after the oxygen sensor. Hence, the closed-loop mixture control done by the ECU was not affected.

THIS paper outlines the status and trends of atmospheric pollution in Finland caused by motor vehicles and evaluates the effect of the current regulatory policy. Details of new emission regulations for passenger cars and heavy duty vehicles are given. Research activities and items of particular concern like the effect of low ambient temperature on emissions are also discussed.

A low ambient temperature increases wear and fuel consumption in vehicle engines. The startability of the engine and the start-up of lubrication are highly dependent on the type of engine oil (mineral, semisynthetic, synthetic), whereas fuel consumption depends more on the engine type and driving conditions. The research work in a special cold chamber equipped with a powerful cooling system has so far involved three gasoline engines and two diesel engines. One gasoline engine was also tested in combination with an all-mechanical transaxle. Tests were carried out within the temperature range of +20…−30 °C using different engine lubricants in order to evaluate both lubrication during the initial start-up and fuel consumption during a test period of 30 minutes. Engines were run under both constant and cyclic load. Effects of auxiliary electrical block and oil sump heaters were also studied.