Having been third fastest in the morning session, Grosjean was busy after lunch, completing a full 60-lap race simulation in the Lotus, using Pirelli's soft and hard compounds.

He backed that up with a series of fast laps, setting the benchmark time of 1m22.614s with just minutes remaining, on a set of soft tyres.

Jean-Eric Vergne ended the day second, despite not completing a flying lap following the lunch break. The Toro Rosso stopped and briefly caught fire with an engine problem right before lunch in Barcelona, bringing out the red flag.

While a full race simulation was planned for the afternoon session, the STR7 didn't appear again until within half an hour of the session's end, and was restricted to pitstop practice.

Neither Vergne nor Grosjean will be back in their respective cars for the rest of the test, with Daniel Ricciardo set to take over for Toro Rosso tomorrow, and Kimi Raikkonen jumping into the Lotus.

Sebastian Vettel was one of the big movers of the afternoon session, improving to a 1m23.361s to jump from fourth to third.

Behind Vettel it was Fernando Alonso, who didn't improve on his morning time, focussing instead on a full race simulation using soft and medium compound tyres.

Heikki Kovalainen was fifth thanks to a run on the supersofts, while Kamui Kobayashi improved to sixth before spending most of the afternoon in the pits, the Sauber sidelined by a hydraulic leak.

It was a similar story for seventh-placed Nico Hulkenberg, his Force India stopping with a drive-line problem just minutes after lunch and never reappearing.

Michael Schumacher improved his time slightly, but still finished the day eighth, while Lewis Hamilton failed to improve, finishing ahead of the Williams pair of Bruno Senna and Pastor Maldonado.

Today's times:

Pos  Driver         Team            Time                Laps
 1.  Grosjean       Lotus           1m22.614s           123
 2.  Vergne         Toro Rosso      1m23.126s  +0.512   31
 3.  Vettel         Red Bull        1m23.361s  +0.747   85
 4.  Alonso         Ferrari         1m23.447s  +0.833   124
 5.  Kovalainen     Caterham        1m23.828s  +1.214   104
 6.  Kobayashi      Sauber          1m23.836s  +1.222   77
 7.  Hulkenberg     Force India     1m23.893s  +1.279   33
 8.  Schumacher     Mercedes        1m23.978s  +1.364   79
 9.  Hamilton       McLaren         1m24.111s  +1.497   65
10.  Senna          Williams        1m24.925s  +2.311   48
11.  Maldonado      Williams        1m25.801s  +3.187   20

Autosport.com