Effect of Turbocharger Cut Out on Two-Stroke Marine Diesel Engine Performance and NOx Emissions at Part Load Operation

Abstract

The diesel engine is widely used for marine vessel propulsion due to its relatively high efficiency compared to existing alternative propulsion systems. The majority of these engines are slow speed two stroke ones. Despite the improvement of their efficiency there now exists a demand for drastic reduction of daily fuel oil consumption as a result of the global financial situation and continuously increasing fuel prices. Towards this effort, slow steaming is a promising solution for the drastic reduction of daily and specific fuel consumption when expressed in tn/mile. This requires engine operation in the low load (low speed) range where these engines are not designed to operate for long term. The main problem related to slow-steaming, is the lack of air which has a negative impact on the engine and its subsystems. A promising solution to the problem is turbocharger (T/C) cut-out at low load when more than one T/C exists. In the present work a combined computational and experimental investigation is conducted to evaluate the operation potential of a large two stroke marine diesel engine equipped with two T/Cs using T/C cut-out, for which the specific technology presents various challenges. This is achieved using an in-house engine simulation model and measurements with and without T/C cut-out. From the results it is revealed that using this technique the scavenging air and peak firing pressure increase while the specific fuel consumption decreases. In this way, some major problems related with the long term operation of the engine under low load conditions, i.e. accumulation of carbon deposits on the exhaust gas side and continuous operation of the auxiliary air blowers, are surpassed. Moreover, a theoretical investigation is conducted considering fuel injection retard to minimize the peak firing pressure penalty while taking care to limit the corresponding negative impact on specific fuel consumption. For NOx emissions the effect of T/C cut-out is also considered using tail pipe emission data measured during the official shop tests. From the analysis conducted it has been revealed that the technique of turbocharger cut–out (one of two) is technically feasible and could offer certain advantages when slow-steaming is implemented. Moreover, comparing the calculated with the measured results, it has been revealed that the simulation model successfully estimates engine operation with and without T/C cut-out, being a valuable tool for the engineers to investigate combustion and pollutant formation mechanisms under various engine configurations.

Analysis of Two Stroke Marine Diesel Engine Operation Including Turbocharger Cut-Out by Using a Zero-Dimensional Model

“…Although slow steaming is commonly used in the last years, only limited published works have investigated this specific engine operating phases [41][42][43]. Kyrtatos et al [43] proposed a novel way of evaluating engine performance by comparing service monitored data and thermodynamic model predictions, and they carried out a study for predicting a VLCC main engine performance at slow steaming conditions concluding that a sufficient extrapolation of the compressor map is required in order to avoid errors in simulation results.…”

“…Kyrtatos et al [43] proposed a novel way of evaluating engine performance by comparing service monitored data and thermodynamic model predictions, and they carried out a study for predicting a VLCC main engine performance at slow steaming conditions concluding that a sufficient extrapolation of the compressor map is required in order to avoid errors in simulation results. Hountalas et al [42] studied the effect of one turbocharger unit cut-out (out of two) on the engine performance and it is concluded that retard of fuel injection could be the solution for reducing the cylinder maximum pressure and the associated NOx emissions. In [41], a MVEM was used to investigate the engine performance at low load operation considering the influence of blower activation/deactivation phases and turbocharger cut-out.…”

A novel objective oriented methodology for marine engine–turbocharger matching

“…Ship energy efficiency objective. When the matching procedure objective is to minimise the annual fuel consumption (FC) (calculated by equation (13) for the engine operating profiles shown in Figure 10), the turbocharger with compressor map ID125 was selected for the single turbocharger system. This turbocharger provided the lowest FC, which was found to be 5% lower than the highest calculated FC.…”

“…The engine−turbocharger matching can be a lengthy process for a new marine engine, due to the large number of the involved parameters, 8 which affects the engine transient response, especially at low loads operation, due to the turbocharging system lag. Alternative configurations were proposed for improving the engine performance and transient response including the sequential turbocharging, 9 the two-stage 10,11 turbocharging, the variable geometry turbine turbocharger, 12 the turbocharger cut-out (in cases with multiple turbochargers connected in parallel), 13,14 and the hybrid turbocharger. 15,16 Nonetheless, the single and parallel turbocharging systems are preferred for most of the marine engines, as they constitute solutions of lower complexity, thus imposing less challenges for their installation, control and maintenance.…”

Investigation of the adverse effects of slow steaming operations for ships

“…As a solution, cutting out of a turbocharger supplies a relatively high amount of exhaust gas flow that increases the operating efficiency of the turbine at the engines with more than one turbocharger. 24 The turbocharger cut-out method had been studied for performance analysis 25 and calculation of the energy efficiency design index. 26 To satisfy smooth operation for turbochargers variable turbine area turbochargers, are another solution to increase the turbocharging efficiency.…”