Search Results

The study of Diesel-HCCI combustion for blended alcohols in Diesel-like fuel was performed in this experimental work to quantify their impact on the net heat release rate. Ethanol and n-butanol were two representative alcohols and were blended with n-heptane; by varying mole percentage from 0, 18, 37 and 57 and varying dilutions with simulated Exhaust Gas Recirculation (EGR) from 0, 20 and 40 percent. The engine speed, intake temperature and equivalence ratio were set at 1500 rpm, 80 °C and 0.3 respectively. The impacts of alcohols were compared with the Primary Reference Fuels by blending n-heptane with iso-octane at the same molar percentage and were tested at same conditions. The results show that blended fuels and dilution with EGR can delay the combustion in different ways. Increasing the EGR rate retards combustion by increasing contained inert species.

In the skyrocketing fuel price situation, using natural gas by means of a diesel dual fuel (DDF) conversion technique is a promising technology as it is flexible for diesel trucks. However, DDF engines suffer from low engine efficiency and poor emission characteristics at low-to-medium load operations. In this study, two DDF concepts were proposed by using five operating parameters including 1) the number of injection pulses, 2) duration of each injection pulse, 3) injection timing, 4) throttle position, and 5) EGR. The first three parameters were varied in the first concept whereas all parameters were varied in the second one. Results from these two DDF conversion concepts were compared to the simple conversion where the operating parameters for diesel injections were fixed by the standard ECU of the OEM. At light load (2000 rpm, 3.1-bar IMEP), the brake efficiencies in the first and the second concepts were improved from the simple conversion by 21% and 35%, respectively.

The effect of high compression ratio on cycle-to-cycle variability was studied using two different combustion chamber shapes, with natural gas operation. A single cylinder Ricardo E6 test engine was run over a range of operating conditions and compression ratios. The different combustion chamber shapes were achieved by using different pistons. At each operating condition detailed cylinder pressure data were recorded for two hundred consecutive cycles allowing for a detailed study of this chaotic phenomenon. The effect of compression ratio on cyclic variation was contradictory for the two combustion chambers, and it is concluded that the real effect was not compression ratio but combustion chamber shape, since the combustion chamber geometry was changed with altering compression ratio for both combustion chambers.

Two heavy duty turbocharged and aftercooled diesel engines have been converted to spark ignition (SI) for natural gas fuelling. One engine features two valves per cylinder, high primary swirl and a compact combustion chamber. The other engine has four valves per cylinder and a more open combustion chamber shape. Both engines were characterized on a dynamometer and subsequently put into service where one of the engines has been monitored extensively. When a diesel engine is converted to SI operation, there is an involved process which must be carried out to insure reliable and efficient operation. Many aspects of the conversion process are limited by the original configuration of the diesel engine. Some of these aspects, such as combustion chamber shape, are shown to be important to the optimization of an SI converted engine and are highlighted in the comparison of these two engines.