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Natural gas (NG)-diesel dual-fuel combustion can be a suitable solution to reduce the overall CO2 emissions of heavy-duty vehicles using diesel engines. One configuration of such a dual-fuel engine can be port injection of NG to form a combustible air-NG mixture in the cylinder. This mixture is then ignited by a direct injection of diesel. Other potential advantages of such an engine include the flexibility of switching back to diesel-only mode, reduced hardware development costs and lower soot emissions. However, the trade-off is lower brake thermal efficiency (BTE) and higher hydrocarbon emissions, especially methane, at low load and/or high engine speed conditions. Advancing the diesel injection timing tends to improve the BTE but may cause the NOx emissions to increase.

Until a proper fueling infrastructure is established, vehicles powered by natural gas must have bi-fuel capability in order to avoid a limited vehicle range. Although bi-fuel conversions of existing gasoline engines have existed for a number of years, these engines do not fully exploit the combustion and knock properties of both fuels. Much of the power loss resulting from operation of an existing gasoline engine on compressed natural gas (CNG) can be recovered by increasing the compression ratio, thereby exploiting the high knock resistance of natural gas. However, gasoline operation at elevated compression ratios results in severe engine knock. The use of variable intake valve timing in conjunction with ignition timing modulation and electronically controlled exhaust gas recirculation (EGR) was investigated as a means of controlling knock when operating a bi-fuel engine on gasoline at elevated compression ratios.

Dedicated natural gas engines suffer the disadvantages of limited vehicle range and relatively few refueling stations. A vehicle capable of operating on either gasoline or natural gas allows alternative fuel usage without sacrificing vehicle range and mobility. However, the bi-fuel engine must be made to provide equal performance on both fuels. Although bi-fuel conversions have existed for a number of years, historically natural gas performance is degraded relative to gasoline due to reduced volumetric efficiency and lower power density of CNG. Much of the performance losses associated with CNG can be overcome by increasing the compression ratio. However, in a bi-fuel application, high compression ratios can result in severe engine knock during gasoline operation. Variable intake valve timing, increased exhaust gas recirculation and retarded ignition timing were explored as a means of controlling knock during gasoline operation of a bi-fuel engine.

Homogeneous Charge Compression Ignition (HCCI) combustion characteristics of dual-stage autoignition fuels were examined over the speed range of 600 to 1700 rpm using a Cooperative Fuels Research (CFR) engine. A fuel vaporizer was used to preheat and partially vaporize the fuel inside the intake plenum. The air and fuel were well-mixed prior to entering the cylinder. Since low temperature heat release (LTHR) is known to be an important factor that affects HCCI combustion of fuels that exhibit dual-stage autoignition behavior, a detailed heat release analyses were performed on both time and crank angle bases. At the lower and upper speeds, the operating ranges were compared as a function of air/fuel ratio (AFR) and exhaust gas recirculation (EGR) from the knocking to misfiring limits. The AFR-EGR operating region was more limited at 1700 rpm than at 900 rpm for the commercial ULSD fuel. Combustion stability was problematic at higher engine speeds.

Reduced emissions, improved fuel economy, and improved performance are a priority for manufacturers of internal combustion engines. However, these three goals are normally interrelated and difficult to optimize simultaneously. Studying the experimental heat release provides a useful tool for combustion optimization. Heavy-duty diesel engines are inherently transient, even during steady state operation engine controls can vary due to exhaust gas recirculation (EGR) or aftertreatment requirements. This paper examines the heat release and the derived combustion characteristics during steady state and transient operation for a 1992 DDC series 60 engine and a 2004 Cummins ISM 370 engine. In-cylinder pressure was collected during repeat steady state SET and the heavy-duty transient FTP test cycles.

The effects of cetane number, aromatics content and 90% distillation temperature (T90) on HCCI combustion were investigated using a fuel matrix designed by the Fuels for Advanced Combustion Engines (FACE) Working Group of the Coordinating Research Council (CRC). The experiments were conducted in a single-cylinder, variable compression ratio, Cooperative Fuel Research (CFR) engine. The fuels were atomized and partially vaporized in the intake manifold. The engine was operated at a relative air/fuel ratio of 1.2, 60% exhaust gas recirculation (EGR) and 900 rpm. The compression ratio was varied over the range of 9:1 to 15:1 to optimize the combustion phasing for each fuel, keeping other operating parameters constant. The results show that cetane number and T90 distillation temperature significantly affected the combustion phasing. Cetane number was clearly found to have the strongest effect.

The exhaust emissions from a single-cylinder version of a heavy-duty diesel engine with exhaust gas recirculation (EGR) were studied using 12 diesel fuels derived from oil sands and conventional sources. The test fuels were blended from 22 refinery streams to produce four fuels (two from each source) at three different total aromatic levels (10, 20, and 30% by mass). The cetane numbers were held constant at 43. Exhaust emissions were measured using the AVL eight-mode steady-state test procedure. PM emissions were accurately modeled by a single regression equation with two predictors, total aromatics and sulphur content. Sulphate emissions were found to be independent of the type of sulphur compound in the fuel. NOx emissions were accurately modeled by a single regression equation with total aromatics and density as predictor variables. PM and NOx emissions were significantly significantly affected by fuel properties, but crude oil source did not play a role.

A comparison of scanning mobility particle sizer (SMPS) and laser-induced incandescence (LII) measurements of diesel particulate matter (PM) was performed. The results reveal the significance of the aggregate nature of diesel PM on interpretation of size and volume fraction measurements obtained with an SMPS, and the accuracy of primary particle size measurements by LII. Volume fraction calculations based on the mobility diameter measured by the SMPS substantially over-predict the space-filling volume fraction of the PM. Correction algorithms for the SMPS measurements, to account for the fractal nature of the aggregate morphology, result in a substantial reduction in the reported volume. The behavior of the particulate volume fraction, mean and standard deviation of the mobility diameter, and primary particle size are studied as a function of the EGR for a range of steady-state engine speeds and loads for a turbocharged direct-injection diesel engine.

The aim of this investigation was to improve understanding and quantify the impact of exhaust gas recirculation (EGR) as an emissions control measure onto cyclic variability of a small-bore, single-cylinder, diesel-fueled compression-ignition (CI) power generation unit. Of special interest were how cycle-to-cycle variations of the CI engine affect steady-state voltage deviations and frequency bandwidths. Furthermore, the study strived to elucidate the impact of EGR addition onto combustion parameters, as well as gaseous and particle phase emissions along with fuel consumption. The power generation unit was operated over five discrete steady-state test modes, representative of nominal 0, 25, 50, 75, and 100% engine load (i.e. 0-484kPa BMEP), by absorbing electrical power via a resistive load bank. The engine was equipped with a passive EGR system that directly connected the exhaust and intake runners through a small passage.

With continuously increasing concern for the emissions from two-stroke engines including regulated hydrocarbon (HC) and oxides of nitrogen (NOx) emissions, non-road engines are implementing proven technologies from the on-road market. For example, four stroke diesel generators now include additional internal exhaust gas recirculation (EGR) via an intake/exhaust valve passage. EGR can offer benefits of reduced HC, NOx, and may even improve combustion stability and fuel efficiency. In addition, there is particular interest in use of natural gas as fuel for home power generation. This paper examines exhaust throttling applied to the Helmholtz resonator of a two-stroke, port injected, natural gas engine. The 34 cc engine was air cooled and operated at wide-open throttle (WOT) conditions at an engine speed of 5400 RPM with fueling adjusted to achieve maximum brake torque. Exhaust throttling served as a method to decrease the effective diameter of the outlet of the convergent cone.

Among the key technologies currently being used for reducing emissions of oxides of nitrogen, Exhaust Gas Recirculation (EGR) has been found to be very effective for light duty diesel engines. However, EGR results in a sharp increase in particulate matter emissions in heavy-duty diesel engines. The presence of increased levels of particulate matter in the engine has led to increased wear of engine parts such as cylinder liners, piston rings, valve train system and bearings. A statistically designed experiment was developed to examine the effects of soot contaminated engine oil on wear of engine components. A three-body wear machine was designed and developed to simulate and estimate the extent of wear. The three oil properties studied were phosphorous level, dispersant level and sulfonate substrate level. The above three variables were formulated at two levels: High (1) and Low (-1). This resulted in a 23 matrix (8 oil blends).

Lean-burn natural gas engines offer attractively low particulate matter emissions and enjoy higher efficiencies than their stoichiometric counterparts. However, even though oxides of nitrogen emissions can be reduced through operation at lambda ratios of greater than 1.3, catalysts cannot reduce the oxides of nitrogen emissions in the oxidizing exhaust environment. Exhaust Gas Recirculation (EGR) offers the potential to reduce engine out oxides of nitrogen emissions by reducing the flame temperature and oxygen partial pressure that encourages their formation during the combustion process. A comparative study involving a change in the nature of primary diluent (air replaced by EGR) in the intake of a Hercules, 3.7 liter, lean-burn natural gas engine has been undertaken in this research. The Hercules engine was equipped with a General Motors electronically controlled EGR valve for low EGR rates, and a slide valve, constructed in house, for high EGR rates.

In North America, heavy-duty diesel engines for on-road use have to meet strict regulations for their emissions of nitric oxide and nitrogen dioxide (cumulatively referred to as ‘NOx’) besides other criteria pollutants. Over the next decade, regulations for NOx emissions are expected to becoming more stringent in North America. One of the major technical barriers for achieving in-use NOx emissions commensurate with the levels determined from in-laboratory test procedures required by regulations is controlling NOx emissions during cold start and engine idling. Since the exhaust gas temperature can be low during these conditions, the effectiveness of the exhaust after-treatment (EAT) system may be reduced. Under colder climate conditions like in Canada, the impact may be even more significant.

Due to tightening emission legislations, both within the US and Europe, including concerns regarding greenhouse gases, next-generation combustion strategies for internal combustion diesel engines that simultaneously reduce exhaust emissions while improving thermal efficiency have drawn increasing attention during recent years. In-cylinder combustion temperature plays a critical role in the formation of pollutants as well as in thermal efficiency of the propulsion system. One way to minimize both soot and NOx emissions is to limit the in-cylinder temperature during the combustion process by means of high levels of dilution via exhaust gas recirculation (EGR) combined with flexible fuel injection strategies. However, fuel chemistry plays a significant role in the ignition delay; hence, influencing the overall combustion characteristics and the resulting emissions.

Heavy-duty diesel (HDD) engines are the primary propulsion source for most heavy-duty vehicle freight movement and have been equipped with an array of aftertreatment devices to comply with more stringent emissions regulations. In light of concerns about the transportation sector's influence on climate change, legislators are introducing requirements calling for significant reductions in fuel consumption and thereby, greenhouse gas (GHG) emission over the coming decades. Advanced engine concepts and technologies will be needed to boost engine efficiencies. However, increasing the engine's efficiency may result in a reduction in thermal energy of the exhaust gas, thus contributing to lower exhaust temperature, potentially affecting aftertreatment activity, and consequently rate of regulated pollutants. This study investigates the possible utilization of waste heat recovered from a HDD engine as a means to offset fuel penalty incurred during thermal management of SCR system.

Most transient heavy duty diesel emissions data in the USA have been acquired using the Federal Test Procedure (FTP), a heavy-duty diesel engine transient test schedule described in the US Code of Federal Regulations. The FTP includes both urban and freeway operation and does not provide data separated by driving mode (such as rural, urban, freeway). Recently, a four-mode engine test schedule was created for use in the Advanced Collaborative Emission Study (ACES), and was demonstrated on a 2004 engine equipped with cooled Exhaust Gas Recirculation (EGR). In the present work, the authors examined emissions using these ACES modes (Creep, Cruise, Transient and High-speed Cruise) and the FTP from a Detroit Diesel Corporation (DDC) Series 60 1992 12.7 liter pre-EGR engine. The engine emissions were measured using full exhaust dilution, continuous measurement of gaseous species, and filter-based Particulate Matter (PM) measurement.

Use of natural gas-diesel dual-fuel (NDDF) combustion in compression ignition engines is a method of reducing the net greenhouse gas (GHG) and particulate matter (PM) emissions of these engines. Compressed natural gas (NG) is injected into the intake manifold of the engine and the air-NG mixture is ignited by a direct injection of diesel in the cylinder. One of the main challenges with NDDF combustion is the methane (primary component of NG) slip at low and medium loads, which reduces the engine efficiency and offsets the advantage of lower carbon dioxide emissions of the NG combustion. In order to address this issue, an intake manifold insert is devised with the objective to alter the intake flow profile into the engine and ultimately reduce the methane slip. This is a novel strategy for an NDDF engine since modifying the in-cylinder flow profile can intensify the mixing between diesel and air-NG mixture in order to improve the NG utilization in the cylinder.