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Recent approval of emission standards for small utility engines by the California Air Resources Board(1)* suggests that substantial reductions in emissions from small utility engines will soon be required. While 1994 standards may be met with simple engine adjustments or modifications, 1999 standards are much more stringent and may require the use of catalysts in conjunction with other emission reduction technologies. Assessing the feasibility of candidate emission control strategies is an important first step. Various emission reduction technologies were applied to three different 4-stroke engines. Emission tests were conducted to determine the effectiveness of air/fuel ratio changes, thermal oxidation, exhaust gas recirculation, and catalytic oxidation with and without supplemental air. Results of these evaluations, along with implications for further work, are presented. One engine's emissions were reduced below the levels of 1999 ARB standards.

Measurement of emissions from small utility engines has usually been accomplished using steady-state raw emissions procedures such as SAE Recommended Practice J1088. While raw exhaust measurements have the advantage of producing modal exhaust gas concentration data for design feedback; they are laborious, may influence both engine performance and the emissions themselves, and have no provision for concurrent particulate measurements. It is time to consider a full-dilution procedure similar in principle to automotive and heavy-duty on-highway emission measurement practice, leading to improvements in many of the areas noted above, and generally to much higher confidence in data obtained. When certification and audit of small engine emissions become a reality, a brief dilute exhaust procedure generating only the necessary data will be a tremendous advantage to both manufacturers and regulatory agencies.

Several properties of a refinery “straightrun kerosene“, which had a narrow boiling range approximating the middle of a No. 1 diesel fuel, were altered to study their effects on regulated and unregulated exhaust emissions. Eleven fuel blends, representing changes in nitrogen content, aromatic level, boiling point distribution, olefin content, and cetane number, were evaluated in a 1975 Mercedes-Benz 240D. Statistical analysis, including regression, was performed using selected fuel properties as independent variables. Higher aromatic levels were generally associated with increased emissions, while increased olefin levels were generally associated with decreased emissions.

In an attempt to characterize emissions from small air-cooled utility engines, five gasoline-fueled models were operated over a variety of speeds and loads, and important exhaust constituents were measured. These emissions included hydrocarbons, CO, CO2, NO, O2, aldehydes, light hydrocarbons, particulates, and smoke. Emissions of SOx were estimated on the basis of the fuel consumed; evaporative losses of hydrocarbons were also estimated. The impact of small engine emissions was calculated on the basis of the test results and information on national engine populations and usage. From these data, it appears that the 50 million or more small engines currently being used account for only a small part of pollutants from all sources.

The research program on which this paper is based included both laboratory emission measurements and extrapolation of results to the national population of heavy-duty farm, construction, and industrial engines. Emission tests were made on four gasoline engines and eight diesel engines typical of those used in F, C, and I equipment. Gaseous and particulate emissions were measured during engine operation on well-accepted steady-state procedures, and diesel smoke was measured during both steady-state conditions and the Federal smoke test cycle. Emissions measured were hydrocarbons, CO, CO2, NO, NOx, O2, aliphatic aldehydes, light hydrocarbons, particulate, and smoke. Emission of sulfur oxides (SOx) was estimated on the basis of fuel consumed, and both evaporative and blowby hydrocarbons were also estimated where applicable (gasoline engines only). Data on emissions obtained from this study were compared with those available in the literature, where possible.

Seven motorcycles, ranging in size from 100 to 1200 cm3, were tested for emissions characterization purposes. They were operated on the federal seven-mode test procedure (for 1971 and older light-duty vehicles), the federal LA-4 test procedure (for 1972 and later LDVs), and under a variety of steady-state conditions. Four of the machines tested had 4-stroke engines, and the other three had 2-stroke engines. Emissions which were measured included hydrocarbons, CO, CO2, NO, NOx, O2, aldehydes, light hydrocarbons, particulates, and smoke. Emissions of SOx were estimated on the basis of fuel consumed, and evaporative hydrocarbon losses were also estimated. Crankcase “blowby” emissions from one 4-stroke machine were measured. The impact of motorcycles on national pollutant totals was estimated, based on the test results and information from a variety of sources on national population and usage of motorcycles.

This paper describes a research program on exhaust emissions from snowmobile engines, including both emissions characterization and estimation of national emissions impact. Tests were conducted on three popular 2-stroke twins and on one rotary (Wankel) engine. Emissions that were measured included total hydrocarbons, (paraffinic) hydrocarbons by NDIR, CO, CO2, NO (by two methods), NOx, O2, aldehydes, light hydrocarbons, particulate, and smoke. Emissions of SOx were estimated on the basis of fuel consumed, and evaporative hydrocarbons were projected to be negligible for actual snowmobile operation. During emissions tests, intake air temperature was controlled to approximately -7°C (20°F), and room air at approximately 24°C (75°F) was used for engine cooling. Based on test results and the best snowmobile population and usage data available, impact of snowmobile emissions on a national scale was computed to be minimal.

To characterize exhaust emissions from water-cooled 2-stroke outboard motors (the predominant type), four new motors were tested on dynamometer stands. The engines ranged from 4-65 hp in size, and operating conditions were chosen along lines of simulated boat loading. All the measurements were taken at steady-state conditions. Emission concentrations were measured in raw exhaust gas and after the gases had been bubbled through water in a specially constructed tank. Constituents measured included hydrocarbons, CO, CO2, NO, NOx, O2, light hydrocarbons, and aldehydes. Emissions of sulfur oxides (SOx) were estimated on the basis of fuel consumed, and all the exhaust emissions data were used with available information on population and usage of motors to estimate exhaust emission factors and national exhaust emissions impact.

Particulate and gaseous emissions from two light-duty diesel vehicles were measured over eight operating schedules, using five different fuels. Characterization included regulated exhaust emissions and a number of unregulated constituents. Non-routine gas measurements included phenols, hydrocarbon boiling range, and aldehydes. Particulate characterization included mass rates and concentrations, visible smoke, aerodynamic sizing, total organics, BaP, sulfate, phenols, trace elements, and major elements. Statistical analysis of emissions data was undertaken using fuel properties and operating schedule statistics as independent variables. Regressions were computed for a few variables, and analysis of variance and multiple comparisons were used where the data were not suitable for regression analysis.

Exhaust emission data from several fuel effects studies were normalized and subjected to statistical analyses. The goal of this work was to determine whether emission effects of property variation in alternate-source fuels were similar, less pronounced, or more pronounced than the effects of property variation in petroleum fuels. A literature search was conducted, reviewing hundreds of studies and finally selecting nine which dealt with fuel property effects on emissions. From these studies, 15 test cases were reported. Due to the wide variety of vehicles, fuels, test cycles, and measurement techniques used in the studies, a method to relate them all in terms of general trends was developed. Statistics and methods used included bivariate correlation coefficients, regression analysis, scattergrams and goodness-of-fit determinations.

Methods for measurement and expression of crankcase or “blowby” emissions from diesels were developed and demonstrated on a test engine. These methods were subsequently used to characterize gas and particulate emissions from two in-service engines. Crankcase emissions were evaluated under engine operating conditions corresponding to the EPA 13-mode certification test. Substances for which analyses were conducted included regulated pollutants, sulfate, trace elements, nitrosamines, individual hydrocarbons, and aldehydes. Emissions from the diesel crankcases were compared to exhaust emissions (where possible) to assess their importance. Analysis for nitrosamines was continued beyond the original effort, utilizing another test engine.

To determine the effects of ambient conditions on emissions from light-duty diesels, 174 emission tests were conducted on four vehicles. The major program objective was estimation of a factor to correct NOx emissions to a standard humidity. Other emissions and ambient conditions were also examined for relationships by regression analysis. Humidity effects on NOx emissions were found to be substantial and quite predictable. Relationships observed between other emissions and ambient conditions were relatively weak and unpredictable. Several types of NOx-humidity correction factors were estimated and compared to those already used for other vehicle and engine classes.

Emissions from a Stirling engine-powered 1986 model light-duty truck were measured using current EPA (chassis dynamometer) emissions certification procedures and certain specialized tests. Three fuels were used including unleaded gasoline, a blend of MTBE in unleaded gasoline, and JP-4. City (FTP) cycles and Highway (FET) cycles were run on all three fuels, and emissions measured during the cycles included hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx). Fuel economy was also calculated for these tests. Additional pollutants measured during some of the tests included aldehydes, 1,3-butadiene, individual hydrocarbon species, and total particulate matter. In addition to the cyclic schedules, steady-state conditions were run on JP-4 and straight gasoline for regulated emissions and fuel economy. The conditions consisted of several simulated gradients at three vehicle speeds, plus idle.

The influence of fuel composition on exhaust emissions from four 1982 model light-duty diesel vehicles was studied on the FTP cycle and at two steady-state conditions, but only the FTP results are presented and discussed in this paper. Nine test fuels were blended specifically for the program, with intentional variation in aromatic content, 90% boiling point, and 10% boiling point. Limited data were also acquired with injection timing at advanced and retarded settings, in addition to the main body of data taken with the engines adjusted to recommended timing. A comparatively small effort was also made to evaluate a tenth fuel consisting of a blend of two of the original nine fuels. Of the fuel characteristics varied intentionally, aromatic content generally had the greatest effect on most emissions of major interest (hydrocarbons, oxides of nitrogen, particulate, soluble organic fraction, polynuclear aromatic hydrocarbons, and mutagenicity of extract by Ames bioassay).

Small engines which are friendly toward the environment are needed all over the world, whether the need is expressed in terms of energy efficiency, useful engine life, health benefits for the user, or emission regulations enacted to protect a population or an ecologically-sensitive area. Progress toward the widespread application of lower-impact small engines is being made through engine design, matching of engine to equipment and task, aftertreatment technology, alternative and reformulated fuels, and improved lubricants. This paper describes three research and development projects, focused on the interrelationships of fuels, lubricants, and emissions in Otto-cycle engines, which were conducted by Southwest Research Institute. All the work reported was funded internally as part of a commitment to advance the state of small engine technology and thus enhance human utility.

A major gap exists in available baseline emissions data on the small utility engine population between the mid-1970's and present day. As part of the input required for a standard-setting process, the California Air Resources Board has funded limited laboratory emission measurements on a number of modern small engines, both 2-stroke and 4-stroke designs. Exhaust constituents characterized in this study include total hydrocarbons, reactive hydrocarbons (RHC), methane, CO, NOx, CO2, O2, aldehydes, and particulate matter. A total of nine engines were evaluated, spanning the range from the smallest widely-used 2-strokes (about 20 cc displacement) to 4-strokes approaching 20 hp.