Robert L. Evans

Improving emissions and performance characteristics of lean burn natural gas engines through partial stratification

Abstract A partially stratified charge (PSC) engine concept has been developed to improve the combustion process in a spark ignition engine fuelled by natural gas, operating at lean air-fuel ratios. In general, this technique is effective at increasing fuel conversion efficiency and brake mean effective pressure at relative air-fuel ratios greater than λ = 1.5. Preliminary testing at 2500r/min showed that PSC reduced combustion duration by almost 10 per cent at a given air-fuel ratio. It was also effective in extending the lean limit of engine operation, which meant that the engine could be run at lower loads without throttling. PSC technology provides an alternative method of load control to throttling, and hence reduces associated pumping losses. Further investigation was conducted at 1500 r/min and a lean air-fuel ratio of λ = 1.65. PSC was found to significantly improve engine performance when compared with homogeneous charge operation at the same air-fuel ratio. The optimized data were compared to simple throttled and lean baseline data and a dramatic reduction in NOx emissions was observed, with little efficiency penalty. These initial results demonstrate that the lean-burn, partially stratified charge strategy is a viable means of engine control, and has significant performance and emissions benefits.

Automotive engine alternatives

How Shall We Power Tomorrows Automobile?.- A Review of the Stratified Charge Engine Concept.- The Dual Fuel Engine.- Automotive Applications of Stirling Engines.- The Development Status of an Automotive Stirling Engine.- The Adiabatic Engine for Advanced Automotive Applications.- Low Heat Rejection Diesel Engines.- Present Status and Future View of Rotary Engines.- The Stratified Charge Rotary Engine.- Turbo-Compound Diesel Engines.- Recent Advances in Variable Valve Timing.- The Outlook for Conventional Automotive Engines.

Fast-Burn Combustion Chamber Design for Natural Gas Engines

The work presented in this paper compares the performance and emissions of the UBC Squish-Jet fast-burn combustion chamber with a baseline bowl-in-piston (BIP) chamber. It was found that the increased turbulence generated in the fast-burn combustion chambers resulted in 5 to 10 percent faster burning of the air-fuel mixture compared to a conventional BIP chamber. The faster burning was particularly noticeable when operating with lean air-fuel mixtures. The study was conducted at a 1.7 mm clearance height and 10.2:1 compression ratio. Measurements were made over a range of air-fuel ratios from stoichiometric to the lean limit. At each operating point all engine performance parameters, and emissions of nitrogen oxides, unburned hydrocarbons, and carbon monoxide were recorded. At selected operating points a record of cylinder pressure was obtained and analyzed off-line to determine mass-burn rate in the combustion chamber. Two piston designs were tested at wide-open throttle conditions and 2000 rpm to determine the influence of piston geometry on the performance and emissions parameters. The UBC squish-jet combustion chamber design demonstrates significantly better performance parameters and lower emission levels than the conventional BIP design. Mass-burn fraction calculations showed a significant reduction in the time to burn the first 10 percent of the charge, which takes approximately half of the time to burn from 10 to 90 percent of the charge.

Fluid Flow in the Squish-Jet Combustion Chamber

Abstract Fluid flow characteristics near top dead centre (TDC) were measured in three different combustion chambers designed to generate squish flow and to enhance turbulence generation in internal combustion engines. One of the combustion chambers was a plain bowl-in-piston type, whereas the remaining two were different configurations of the squishjet chamber, which has a unique geometry for forming jets that converge radially inwards as TDC is approached. Both particle image velocimetry (PIV) and laser Doppler velocimetry (LDV) were used to measure mean velocities and turbulent fluctuations near to TDC. To accurately and consistently set the initial and boundary conditions, the University of British Columbia Rapid Intake and Compression Machine (UBC-RICM) was used. The microscopic particles used for PIV and LDV seeding were introduced into the cylinder by a novel system developed to suit the momentary flow in the UBC-RICM. The experimental study led to a greater understanding of the flow processes inside these complex combustion chambers. The results also indicated that squish-jet chambers tend to generate higher levels of turbulence than plain bowl-in-piston chambers do, even though they may generate lower mean squish velocities. These results will also be used in a future study to assess the validity of squish flow predictions made by the computational fluid dynamic code, KIVA-3V.

A numerical and experimental study of the squish-jet combustion chamber

Abstract The fluid flow characteristics near top dead centre (TDC) were numerically simulated for three different combustion chambers designed to generate squish flow and enhance turbulence generation in spark ignition engines. One of the combustion chambers was a plain bowl-in-piston type while the remaining two were different configurations of the squish-jet chamber, which has a unique geometry for forming jets that converge radially inwards as TDC is approached. The computational fluid dynamics (CFD) code KIVA-3V was used to produce the simulations and particular attention was given to mean velocities and turbulent fluctuations near TDC. The flow fields were measured experimentally (with particle image velocimetry (PIV) and laser Doppler velocimetry (LDV)) in a unique rapid-intake and compression machine, and compared with the output from the KIVA-3V code. The use of the rapid-intake and compression machine enabled the initial conditions to match exactly those in the KIVA-3V calculations, thus reducing uncertainty in the validation study. The study led to a greater understanding of the flow processes inside these complex combustion chambers and the results showed that squish-jet chambers tend to generate higher peak turbulence levels than do plain bowl-in-piston chambers, even though they may generate lower mean squish velocities. From this perspective, the KIVA code can be a useful tool for designing squish-jet combustion chambers. The study also showed that KIVA-3V predicted downstream squish jet velocities well. Nevertheless, the squish-jet velocities at the piston bowl rim were overestimated and the specific turbulent kinetic energy (k) and its dissipation (e) appear to have been overestimated during much of the compression period tested.

Energy Conversion Chain Analysis of Sustainable Energy Systems: A Transportation Case Study

In general terms there are only three primary energy sources: fossil fuels, renewable energy, and nuclear fission. For fueling road transportation, there has been much speculation about the use of hydrogen as an energy carrier, which would usher in the “hydrogen economy.” A parallel situation would use a simple battery to store electricity directly in order to power vehicles. The efficiency of these two different approaches has been compared and shows that the hydrogen and fuel cell system would consume nearly three times the primary energy required by a battery storage system. Successful introduction into the marketplace of the plug-in hybrid vehicle would eliminate the need for road vehicles to use petroleum fuels, at least for the majority of miles traveled. If electricity were to be generated primarily from sustainable primary energy sources, then road transportation would also become sustainable, resulting in an “electricity economy” rather than a “hydrogen economy.”

Hydrogen Economy or Electricity Economy?: A Transportation Case Study

Transportation accounts for more than a quarter of total global energy consumption. For fuelling road transportation there has been much speculation about the use of hydrogen as an energy carrier, which proponents claim would usher in the “Hydrogen Economy”. The concept of the “complete energy conversion chain” has been used to compare the overall energy consumption and CO2 emissions from vehicles powered by hydrogen fuel cells with those from vehicles using a battery and electric drive. The analysis shows that if a sustainable source of electricity is used to produce hydrogen, then the hydrogen and fuel cell system is just equivalent to a battery. The efficiency of these two different approaches has been compared, and shows that the hydrogen system would consume nearly three times the primary energy required by a battery storage system. Conventional batteries do not, however, have a sufficiently high energy storage density to provide the range needed for most drivers. A new generation of plug-in hybrid vehicles is being developed which take advantage of the best attributes of both electric vehicles and conventional fossilfuelled vehicles. These vehicles show promise to dramatically reduce the quantity of greenhouse gases produced each year by the transportation sector.© 2009 ASME

Extending the Lean Limit of Natural Gas Engines

Two different methods to improve the thermal efficiency and reduce the emissions from lean-burn natural gas fuelled engines have been developed, and are described in this paper. One method used a “squish-jet” combustion chamber designed specifically to enhance turbulence generation, while the second method provided a partially stratified-charge mixture near the spark plug in order to enhance the ignition of lean mixtures of natural gas and air. The squish-jet combustion chamber was found to reduce Bsfc by up to 4.8% in a Ricardo Hydra engine, while the NOx – efficiency tradeoff was greatly improved in a Cummins L-10 engine. The partially stratified-charge combustion system extended the lean limit of operation in the Ricardo Hydra by some 10%, resulting in a 64% reduction in NOx emissions at the lean limit of operation. Both techniques were also shown to be effective in increasing the stability of combustion, thereby reducing cyclic variations in cylinder pressure.© 2008 ASME