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In light of forthcoming particle number legislation for light-duty passenger vehicles, time-resolved Particle Mass (PM) and Particle Number (PN) emissions over the New European Drive Cycle (NEDC) are reported for four current vehicle technologies; modern diesel, with and without a Diesel Particulate Filter (DPF), Direct Injection Spark Ignition (DISI) gasoline and multi-point Port Fuel Injection (PFI) gasoline. The PN and PM emissions were ordered (highest to lowest) according to: Non-DPF diesel ≻ DISI ≻ PFI ~ DPF diesel. Both the non-DPF diesel and DISI vehicles emitted PN and PM continuously over the NEDC. This is in contrast with both the DPF diesel and PFI vehicles which emitted nearly all their PN and PM during the first 200 seconds. The PFI result is thought to be a consequence of cold-start mixture preparation whilst several possible explanations are offered for the DPF diesel trend.

A number of tests were conducted on a 2.5 litre, high-speed, direct-injection diesel engine running at various loads and speeds. The aim of the tests was to gain understanding which would lead to more effective use of exhaust gas recirculation (EGR) for controlling exhaust NOx whilst minimising the penalties of increased smoke emission and fuel consumption. In addition to exhaust emission measurements, in-cylinder sampling of combustion gases was carried out using a fast-acting, snatch-sampling valve. The results showed that the effectiveness of EGR was enhanced considerably by cooling the EGR. In addition to more effective NOx control, this measure also improved volumetric efficiency which assisted in the control of smoke emission and fuel consumption. This second of two papers on the use of EGR in diesel engines deals with the effects of EGR on soot emission and on the engine fuel economy.