Evaluation of exhaust gas recirculation techniques on a high-speed direct injection diesel engine using first law analysis

Abstract

The effects of different exhaust gas recirculation (EGR) strategies on engine efficiency and the resulting energy flows at two speed/load conditions (1500 r/min/6.8 bar net indicated mean effective pressure (nIMEP) and 1750 r/min/13.5 bar nIMEP) were studied using a first law analysis approach. The EGR strategies tested were as follows: cooled high-pressure exhaust gas recirculation (baseline), the application of exhaust gas recirculation with the swirl flap closed and the use of exhaust gas recirculation under constant λ conditions. The closed swirl flap exhaust gas recirculation strategy reduced brake efficiency under high load conditions and increased heat transfer to the coolant for both load cases. Soot and CO emissions increased at high load, however, with an increase in NOx relative to the baseline case. The constant λ exhaust gas recirculation strategy reduced brake efficiency under low load, as well as the heat flow to the coolant for both load cases. The constant λ exhaust gas recirculation strategy benefited smoke emissions and increased combustion exhaust gas recirculation tolerance, albeit with a penalty in NOx emission.

Thermal Analysis of Steel and Aluminium Pistons for an HSDI Diesel Engine

“…The instrumentation used in this work has been presented in detail in previous studies [3]. Crank-angle resolved cylinder pressure data were measured using a piezoelectric Kistler transducer and logged with a high-speed data acquisition unit, AVL Indicom at a resolution of 0.1 CAD.…”

“…Low frequency channels (at 1 Hz) were logged using the CADET engine control system by Sierra-CP engineering. Highaccuracy differential thermocouples, employed in past studies [3],were used to measure the small coolant temperature differences observed across the engine. Blowby measurements were made with an Amber Instruments VF563 series flowmeter.…”

“…Note that, as discussed below, the effect of blowby gases on the overall energy balance calculations was expected to be negligible and that blowby is therefore not considered in the model. The first law analysis model is described in detail in a previous study [3]. The chemical energy of the exhaust gases is calculated from the oxidation energy of CO, H 2 and total hydrocarbon (THC) species, with the THCs assuming to have the same composition as the input fuel.…”

“…Brake and indicated work are calculated in this work by using a load cell and the in-cylinder pressure trace respectively with their difference indicating the total losses due to friction and work required to drive ancillary components. In the current work, ancillary losses are restricted to the parasitic torque of the high pressure pump-this calculation is detailed in a previous study [3]. As described in this earlier work, the fuel pump is sourced from a production fourcylinder engine.…”

“…Upcoming CO 2 emission limits -95 g/km in Europe by 2021 and 97 g/km in America by 2025 [1] have led automotive manufacturers to explore a wide variety of methods to increase thermal efficiency. Studies have shown that between 10 to 25% of the fuel energy released in-cylinder is transferred to the cylinder walls (depending on load conditions)and then to the engine coolant and oil [2,3]. Reducing this heat transfer thus has great potential for delivering significant improvements in thermal efficiency.…”